Compressing device and method, decompressing device and method, compressing/decompressing system, program, record medium

ABSTRACT

A compressing device comprises plural stages of delay circuits ( 1   -1  to  4   -1 ) and multiplying/adding circuits ( 5   -1  to  10   -1 ) that performs weighted addition of output data from the delay circuits ( 1   -1  to  4   -1 ) according to the value of a digital basic function and thereby determines thinned-out data from sampling data sequentially inputted. Since the thinned-out data is determined by the compression part using a digital basic function serving as the original of a sampling function of infinite supports defferentiable once or more times over the whole range, a compression ratio of at lease 8 can be achieved only by the simple four operations. Further, since interpolation data is determined by the decompression part by using the same digital basic function, the original data before the compression can be reproduced with substantial fidelity by only the simple four operations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressing device and method, adecompressing device and method, a compressing/decompressing system, aprogram, and a record medium and particularly concerns methods ofcompressing and decompressing successive analog signals or discretedigital signals.

2. Description of the Related Art

Conventionally, in case of transmitting and accumulating a signal suchas an image signal and an aural signal having a large amount ofinformation, signals have been compressed and decompressed in order toreduce an amount of transmitted information and increase storable timein a storage medium. In general, when an analog signal is compressed,the analog signal is firstly sampled according to a predeterminedsampling frequency and is digitalized, and a compressing operation isperformed on obtained digital data.

Thinning compression has been present as an example of the compressingoperation. The most simple method of thinning compression is that dataon a predetermined sample point is discarded from all the sample points(conversely, only data on the predetermined sample point is used). Forexample, a double compression ratio can be achieved by adopting data onalternate sample points. When a compression ratio can be increased, datais used on every n^(th) (>2) sample points.

According to this method, although signals can be compressed withoutperforming any operations at all, decompression causes a problem ofreproducibility to the original data. Namely, on the decompression part,data between sample points adopted during compression is obtained by aninterpolating operation. More data are discarded on sample points thatare originally required for accurately reproducing the original data asadopted sample points have a larger interval to increase a compressionratio. Thus, reproducibility to the original data is considerablydegraded.

For this reason, in order to attain both of an improved compressionratio and reproducibility to the original data, an amount of informationis normally thinned out by performing some operation on data on samplepoints. For example, a method of replacing data A and B on two adjacentsample points with an average data (A+B)/2 is available. With thismethod, unlike the case where one of the original data A and B iscompletely abandoned, since data added with both of the original data Aand B is adopted as compression data (thinned-out data), reproducibilityto the original data is somewhat improved.

However, such an operation cannot obtain any preferable reproducibilitysufficiently for practical use. In order to increase a compression ratioand obtain data reproducibility sufficiently for practical use, morecomplicated operations are necessary.

Further, when thinning compression is performed, return noise is causedby degraded frequency characteristics and degrades the quality ofsignals obtained by decompression.

As described above, it has been extremely difficult to improve both of acompression ratio and the quality of reproduced data. In such a state,methods of compression and decompression for performing complicatedoperations are currently used instead of simple thinning compression inmany cases.

For example, for compression of an image signal and an aural signal, thefollowing method is used: after the original data is processed by usinga conversion filter of a time axis—frequency axis of a DCT(Discreat-Cosine-Transform) and so on, compression is performed in afrequency area. DPCM (Differential Pulse Code Modulation) frequentlyused as a compressing method of an aural signal on a telephone line hasbeen used in consideration of this point. Besides, the compressingmethod of DPCM is a method of coding a difference between adjacentsample values when a waveform is sampled.

As a method of time/frequency conversion, a method using a sub-bandfilter and MDCT (Modified Discrete Cosine Transform) is available, andMPEG (Moving Picture Image Coding Experts Group) audio is available as acoding method using such a method.

Further, an image compressing system used most widely has been generallyknown as an MPEG standard.

A decompressing operation for data compressed according to the abovecompressing method is basically performed according to the reversedoperation of the compressing operation of the same compressing method.

Namely, compressed digital data is converted from a signal of afrequency area to a signal of a time area by frequency/time conversionprocessing, and then, a predetermined decompressing operation isperformed, so that the original digital data is reproduced. Then, theoriginal data obtained thus is subjected to digital-analog conversion atneed, and the data is outputted as an analog signal.

In recent years, an amount of information has increased as an imagesignal and an aural signal become finer, and information communicationusing a mobile terminal, an Internet, and so on has become widespread.Thus, a higher compression ratio and the higher quality of reproduceddata have been demanded increasingly. However, although improvement hasbeen made in the above described conventional compressing anddecompressing methods using DCT or the like, there is a limit on ahigher compression ratio and reproduced data with higher quality. Hence,it has been extremely difficult to realize a higher compression ratioand higher quality.

Further, in the above described conventional compressing anddecompressing methods, since a signal on a time base is converted to asignal on a frequency axis before compression, processing such astime/frequency conversion during compression and frequency/timeconversion during decompression is necessary. Thus, there is a problemthat the processing is complicated and the configuration for theprocessing is extremely complicated, resulting in difficulty inachieving a smaller device as well as longer processing time ofcompression and decompression.

The present invention is achieved to solve the above-described problemsand has as its objective the provision of completely new compressing anddecompressing methods of improving a compressing ratio and the qualityof reproduced data.

Moreover, the present invention is also aimed to simplify thecompressing and decompressing operations of a signal to shortenprocessing time and also simplify the configuration for performing theoperations.

SUMMARY OF THE INVENTION

A compressing device of the present invention is comprising delaycircuits of several stages for sequentially delaying each sampling datainputted therein in sequence, and a multiplying/adding circuit forperforming weighted addition on data outputted from each of the delaycircuits. The weighted addition is performed according to a value of adigital basic function, whereby thinned-out data is produced from thesequentially inputted sampling data.

Another aspect of the present invention is characterized that the delaycircuits of the four stages and the multiplying/adding circuits aredesigned as a thinning-out circuit, and in the compressing device, atleast two thinning-out circuits are connected so as to have a cascadeconnection.

Another aspect of the present invention is characterized in thatsampling data is sequentially inputted therein as a target ofcompression, and then weighted addition is performed on sampling data ona target sample point and sampling data on several sample points aroundthe target sample point, the weighted addition being performed accordingto a value of a digital basic function, whereby thinned-out data isproduced from the sequentially inputted sampling data.

Another aspect of the present embodiment is comprising thinning-outmeans for performing weighted addition with respect to the inputtedsampling data to produce thinned-out data therefrom, in which theweighted addition is performed on sampling data on a target sample pointand sampling data on several sample points around the target samplepoint, the weighted addition being performed according to a value of adigital basic function, sampling point detecting means for detecting asampling point using the thinned-out data produced by the thinning-outmeans, in which a sample point, where an error between each data valueon a straight line connecting two thinned-out data and a thinned-outdata value on the same sample point as that of the data value on thestraight line is equal to or smaller than a predetermined value, isdetected as the sampling point, and compression data producing means forproducing, in the form of compression data, a pair of discrete amplitudedata on each of the detected sampling points and timing data indicatinga time interval between the detected sampling points.

Another aspect of the present invention is further comprising replacingmeans for replacing sampling data with zero data, in which among thediscrete sampling data successively inputted as a target of compression,the sampling data to be replaced has an absolute value smaller than apredetermined value.

Another aspect of the present invention is further comprising replacingmeans for rounding by a predetermined value an absolute value of thesampling data inputted as a target of compression, as well as forperforming a data replacement process, wherein in the data replacementprocess, the replacing means replaces sampling data with zero data, inwhich among the sampling data inputted as a target of compression, thesampling data to be replaced has absolute value smaller than apredetermined value.

Here, the rounding operation is performed by an operation in which datavalues before and after the rounding operation have a non-linearrelationship.

Another aspect of the present invention is further comprising zerocompressing means for performing a zero compressing process with respectto the thinned-out data outputted from the rounding means, wherein thezero compressing process is performed when a predetermined number ormore of data having absolute values of zero are successively outputtedfrom the rounding means, and wherein in the zero compressing process, aset of the predetermined number of zero data is replaced with a pair ofa value of −0 and a value indicating the number of successive zero data,and then the thinned-out data including a replacement result isoutputted from the zero compressing means.

Further, a compressing method of the present invention is characterizedin that regarding sampling data sequentially inputted as a target ofcompression, thinned-out data is obtained from the sequentially inputtedsampling data by performing weighted addition on sampling data on atarget sample point and sampling data on several sample points aroundthe target sample point according to a value of a digital basicfunction.

Another aspect of the present invention is comprising the steps ofsequentially inputting sampling data as a target of compression,performing weighted addition with respect to the inputted sampling data,the weighted addition being performed on sampling data on a targetsample point and sampling data on several sample points around thetarget sample point, and the weighted addition being performed accordingto a value of a digital basic function, whereby thinned-out data isproduced from the sequentially inputted sampling data, determining asampling point using the produced thinned-out data, in which a samplepoint, where a difference value between each data value on a straightline connecting two thinned-out data and a thinned-out data value on thesame sample point as that of the data value on the straight line isequal to or smaller than a predetermined value, is detected as thesampling point, and producing, in the form of compression data, a pairof discrete amplitude data on each of the detected sampling points andtiming data indicating a time interval between the detected samplingpoints.

Another aspect of the present invention is further comprising the stepof replacing sampling data with zero data, in which among the discretesampling data successively inputted as a target of compression, thesampling data to be replaced has an absolute value smaller than apredetermined value.

Another aspect of the present invention is further comprising the stepof rounding lower-order bits of amplitude data on each of the detectedsampling points.

Here, the rounding operation is performed by, for example, an operationin which data values before and after the rounding operation have anon-linear relationship.

Another aspect of the present invention is comprising further comprisingthe step of performing a zero compressing process with respect to thethinned-out data subjected to the rounding operation, wherein the zerocompressing process is performed when a predetermined number or more ofdata having absolute values of zero are successively outputted in therounding operation, and wherein in the zero compressing process a set ofthe predetermined number of zero data is replaced with a pair of a valueof −0 and a value indicating the number of successive zero data, andthen the thinned-out data including a replacement result is outputted.

Moreover, a decompressing device of the present invention is comprisingdelay circuits of several stages into which discrete thinned-out dataproduced by a compressing device claimed in claim 1 can be inputted,each of the delay circuits delaying the inputted thinned-out data insequence, and a multiplying/adding circuit for performing weightedaddition on data outputted from each of the delay circuits, the weightedaddition being performed according to a value of a digital basicfunction, whereby interpolation data for the thinned-out data isproduced.

Another aspect of the present invention is characterized that the delaycircuits and the multiplying/adding circuit are designed as anoversampling circuit, and in the decompressing device, at least twooversampling circuits are connected so as to have a cascade connection.

Another aspect of the present invention is further comprising anaveraging circuit for producing average data of adjacent interpolationdata values outputted from the multiplying/adding circuit.

Another aspect of the present invention is characterized in thatthinned-out data is inputted therein sequentially, and theninterpolation data for the thinned-out data inputted sequentially isproduced by performing weighted addition on thinned-out data on a targetsample point and thinned-out data on several sample points around thetarget sample point, in which the weighted addition is performedaccording to a value of a digital basic function.

Another aspect of the present invention is comprising firstinterpolating means for performing an interpolation process with respectto thinned-out data produced by a compressing device claimed in claim 9,in which in the interpolation process, timing data and amplitude data oneach sampling point are used to produce first interpolation data forinterpolating between one amplitude data and the other amplitude datawhich have a time interval indicated by the timing data, and secondinterpolating means for producing second interpolation data for theproduced first interpolation data by performing a further interpolationprocess with respect to the produced first interpolation data, in whichin the further interpolation process, weighted addition is performed oninterpolation data on a target sample point and interpolation data onseveral sample points around the target sample point, the weightedaddition being performed according to a value of a digital basicfunction.

Another aspect of the present invention is further comprising inverserounding means for performing an inverse rounding operation on amplitudedata on each sampling point in compression data, the inverse roundingoperation being performed in a manner reversed from a rounding operationperformed during compression by the compression device.

Another aspect of the present invention is further comprisinginterpolating means for performing an interpolation process with respectto discrete thinned-out data produced by a compressing device claimed inclaim 15 to produce interpolation data for the discrete thinned-outdata, wherein in the interpolation process, weighted addition isperformed on thinned-out data on a target sample point and thinned-outdata on several sample points around the target sample point, theweighted addition being performed according to a value of a digitalbasic function.

Another aspect of the present invention is further comprising zerodecompressing means for performing a zero decompressing process withrespect to thinned-out data, in which when a −0 value is detected in thethinned-out data, a corresponding number of successive zero data arereproduced through the zero decompressing process.

Further, a decompressing method of the present invention ischaracterized in that regarding discrete thinned-out data, interpolationdata for the discrete thinned-out data is obtained by performingweighted addition on thinned-out data on a target sample point andthinned-out data on several sample points around the target sample pointaccording to a value of a digital basic function.

Another aspect of the present invention is characterized by performingan averaging operation on adjacent interpolation data regardinginterpolation data obtained by performing weighted addition according toa value of the digital basic function.

Another aspect of the present invention is comprising the steps ofperforming a first interpolation, in which in the first interpolationprocess, timing data and amplitude data on each sampling point are usedto produce first interpolation data for interpolating between oneamplitude data and the other amplitude data which have a time intervalindicated by the timing data, and performing a second interpolationprocess with respect to the produced first interpolation data to producesecond interpolation data for the produced first interpolation data, inwhich another weighted addition is performed on first interpolation dataon a target sample point and first interpolation data on several samplepoints around the target sample point, the weighted addition beingperformed according to a value of a digital basic function.

Another aspect of the present invention is further comprising the stepsof performing an inverse rounding operation on amplitude data on eachsampling point in compression data, the inverse rounding operation beingperformed in a manner reversed from a rounding operation performedduring compression by the compressing method.

Another aspect of the present invention is characterized in thatweighted addition is performed with respect to discrete thinned-outdata, wherein the weighted addition is performed on thinned-out data ona target sample point and thinned-out data on several sample pointsaround the target sample point to produce interpolation data for thediscrete thinned-out data, the weighted addition being performedaccording to a value of a digital basic function.

Another aspect of the present invention is further comprising the stepsof performing a zero decompressing process with respect to thinned-outdata produced by a compressing method claimed in claim 36, in which whena −0 value is detected in the thinned-out data, a corresponding numberof successive zero data are reproduced through the zero decompressingprocess.

Further, a program of the present invention is, for example, acompressing program for causing a computer to function as each means asset forth in claim 9, a compressing program for causing the computer toperform the operating steps of a compressing method as set forth inclaim 24, a decompressing program for causing the computer to functionas each means as set forth in claim 66, or a decompressing program forcausing the computer to perform the operating steps of the decompressingmethod as set forth in claim 77.

Further, a record medium readable by a computer according to the presentinvention is characterized by recording, for example, a program forcausing a computer to function as each means as set forth in claim 9, aprogram for causing the computer to perform the operating steps of thecompressing method as set forth in claim 24, a program for causing thecomputer to function as each means as set forth in claim 66, or aprogram for causing the computer to perform the operating steps of adecompressing method as set forth in claim 77.

Moreover, a compressing/decompressing system of the present invention ischaracterized in that on the compression part, regarding sampling datasequentially inputted as a target of compression, thinned-out data isobtained from the sequentially inputted sampling data by performingweighted addition on sampling data on a target sample point and samplingdata on several sample points around the target sample point accordingto a value of a digital basic function, and on the decompression part,regarding thinned-out data inputted in sequence, interpolation data forthe sequentially inputted thinned-out data is obtained by performingweighted addition on thinned-out data on a target sample point andthinned-out data on several sample points around the target sample pointaccording to a value of the digital basic function.

Another aspect of the present invention is characterized in that on thecompression part, data having an absolute value smaller than apredetermined value is replaced with zero data in the sampling datainputted in sequence as a target of compression, and the thinned-outdata is obtained by performing weighted addition on the replaced dataaccording to a value of the digital basic function.

Another aspect of the present invention is characterized in that arounding operation is performed for rounding lower-order bits of theobtained thinned-out data on the compression part, an operation reversedfrom the rounding operation is performed on the sequentially inputtedthinned-out data on the decompression part, and the interpolation datais obtained by performing weighted addition on data after an inverserounding operation according to a value of the digital basic function.

Another aspect of the present invention is characterized in that in therounding operation on the compression part, data values before and afterthe inverse rounding operation have a non-linear relationship, andregarding the obtained thinned-out data after the rounding operation,when a predetermined number or more of data having absolute values ofzero continues, the data are replaced with a pair of a value of −0 and avalue indicating the number of successive zero data and the pair ofvalues is outputted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of acompressing device (thinning-out device) according to Embodiment 1;

FIG. 2 is a diagram showing an example of a configuration of adecompressing device (interpolating device) according to Embodiment 1;

FIGS. 3 is a diagram for explaining thinning and interpolatingprinciples according to Embodiment 1;

FIG. 4 is a diagram showing a digital basic function used in Embodiments1 to 4;

FIG. 5 is a characteristic diagram showing oversampling results obtainedby inputting data of a unit pulse to the decompressing device of FIG. 2;

FIG. 6 is an explanatory drawing showing a sinc function;

FIG. 7 is a diagram showing a frequency characteristic of a samplingfunction of <4> in FIG. 5;

FIG. 8 is a diagram showing another example of the configuration of thedecompressing device according to Embodiment 1;

FIG. 9 is a diagram showing another example of the configuration of thedecompressing device according to Embodiment 1;

FIG. 10 is a diagram showing another example of the configuration of thedecompressing device according to Embodiment 1;

FIGS. 11 is a diagram for explaining thinning and interpolatingprinciples according to Embodiment 2;

FIG. 12 is a diagram showing an example of a configuration of acompressing device (thinning device) according to Embodiment 2;

FIG. 13 is a diagram showing an example of a configuration of adecompressing device (interpolating device) according to Embodiment 2;

FIG. 14 is a diagram showing an example of a configuration of thecompressing device according to Embodiment 3;

FIGS. 15 is a diagram for explaining the basic principle of linearcompression according to Embodiment 3;

FIGS. 16 is a diagram for explaining error operation used in linearcompression according to Embodiment 3;

FIG. 17 is a diagram showing an example of a non-linear roundingoperation according to Embodiment 3;

FIG. 18 is a diagram for explaining another example of the non-linearrounding operation according to Embodiment 3;

FIG. 19 is a diagram showing an example of a decompressing deviceaccording to Embodiment 3;

FIG. 20 is a diagram for explaining an example of a non-linear inverserounding operation according to Embodiment 3;

FIG. 21 is a diagram for explaining another example of the non-linearinverse rounding operation according to Embodiment 3;

FIG. 22 is a waveform chart for comparing the original data beforecompression and reproduced data obtained by decompression whenEmbodiment 3 is adopted;

FIG. 23 is a diagram showing the input/output characteristics of theoriginal data before compression and reproduced data obtained bydecompression when Embodiment 3 is adopted;

FIG. 24 is a chart showing the frequency characteristics ofdecompression data obtained by inputting one compression data producedby the compressing device of FIG. 14 to the decompressing device of FIG.19;

FIG. 25 is a diagram showing an example of a configuration of acompressing device according to Embodiment 4;

FIGS. 26 is a diagram showing an example of the format of compressiondata blocked in Embodiment 4; and

FIG. 27 is a diagram showing an example of a configuration of adecompressing device according to Embodiment 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

The following will discuss Embodiment 1 of the present invention inaccordance with the accompanied drawings.

FIG. 1 is a diagram showing an example of a configuration of acompressing device (thinning device) according to Embodiment 1. FIG. 2is a diagram showing an example of a configuration of a decompressingdevice (interpolating device) according to Embodiment 1. FIGS. 3(a) and3(b) are diagrams for explaining thinning and interpolating principlesaccording to Embodiment 1. FIG. 3(a) shows the thinning principle andFIG. 3(b) shows the interpolating principle.

First, referring to FIG. 3(a), the thinning principle of the presentembodiment will be discussed. In a data structure of FIG. 3(a), thelateral axes of A, B, C, . . . denote sampling data on a sample pointthat is inputted in sequence on each clock and the data values arecoefficients for a digital basic function. Further, the longitudinalaxes of a, b, c, . . . denote center positions of sampling dataprocessed by the digital basic function.

The digital basic function used for this principle is a basic of asampling function used for performing data interpolation of oversamplingand is shown in FIG. 4. The digital basic function is produced bychanging a data value to −1, 1, 8, 8, 1, and −1 on each clock.

As shown in FIGS. 3(a) and 3(b), the digital basic function for samplingdata A is provided by shifting each of the function values (−1, 1, 8, 8,1, −1) by one clock while the first clock position is placed at thefront. Moreover, the digital basic function for the subsequent samplingdata B is provided by shifting each of the function values by one clockwhile a clock position after two clocks from the first clock position isplaced at the front. Similarly, the digital basic functions for samplingdata C, D, E, F, . . . inputted in sequence are provided by shiftingeach of the function values by one clock while a clock position furtherdelayed by two clocks is placed at the front.

In the present embodiment, an operation for thinning out the samplingdata A, B, C, . . . on the sample points to a half is performed based onsuch a data structure. Namely, a predetermined operation is performed oneach pair of adjacent two sampling data of (B, C), (D, E), (F, G) . . .and each pair of the sampling data is replaced with one thinned-out data(B+C)/2, (D+E)/2, (F+G)/2, . . .

The following will discuss an example in which one thinned-out data(B+C)/2 is produced from two adjacent sampling data (B, C). When acenter position b of the sampling data B processed by the digital basicfunction is interposed between two lines of data and the data aredenoted by b1 and b2, b1 and b2 are expressed by the followingequations.b1=A+8B−C   (1)b2=−A+8B+C   (2)

Based on equations (1) and (2), the following equation is established.b=(b1+b2)/2=8B, that is, B=b/8   (3)

Similarly, as to data on a center position c of sampling data C, thefollowing equations are established.c1=B+8C−D   (4)c2=−B+8C+D   (5)c=(c1+c2)/2=8C, that is, C=c/8   (6)

Meanwhile, one thinned-out data (B+C)/2 of the two adjacent data (B, C)is obtained by a convoluting operation of data b2 and data c1. Namely,based on the above equations (2), (3), (4), and (6), the thinned-outdata is expressed by the following equation.(B+C)/2=(b2+c1)/16=((−A+8B+C)+(B+8C−D))/16=(9(B+C)−(A+D))/16   (7)

In this way, the two sampling data B and C can be replaced with onethinned-out data (B+C)/2 expressed by equation (7). The thinned-out datais obtained as follows: from a value obtained by adding the two targetsampling data B and C and multiplying the obtained value by ninesixteenth, a value is subtracted which is obtained by adding the twosampling data A and D adjacent to both sides of the two target samplingdata B and C and multiplying the obtained value by one sixteenth.

Similarly, two sampling data (D, E) are replaced with one thinned-outdata (D+E)/2. The same operation is performed on the succeeding samplingdata (F, G) . . . Besides, since the first sampling data A lacks datarequired for performing the same operation, the state is kept as it iswithout performing the thinning-out operation.

In this way, the same thinning-out operation is performed based on datathinned to a half, so that the original data can be thinned to onefourth. Further, the same thinning-out operation is performed based onthe data thinned to one fourth, so that the original data can be thinnedto one eighth. Theoretically, the original data can be compressed to½^(n) by repeating the same thinning-out operation n times.

Next, referring to FIG. 3(b), the following will discuss the principleof data interpolation according to the present embodiment. In the datastructure of FIG. 3(b), the lateral axes of A, B, C, . . . denotesampling data on a sample point that is inputted in sequence on eachclock and the data values are coefficients of a digital basic function.Further, the longitudinal axes of a, b, c, . . . denote center positionsof thinned-out data processed by the digital basic function. The digitalbasic function used for this principle is also shown in FIG. 4.

As shown in FIG. 3(b), the digital basic function for thinned-out data Ais provided by shifting each of the function values (−1, 1, 8, 8, 1, −1)by one clock while the first clock position is placed at the front. Thedigital basic function for the subsequent thinned-out data B is providedby shifting each of the function values by one clock while a clockposition after two clocks from the first clock position is placed at thefront. Similarly, the digital basic functions for thinned-out data C, D,E, F, . . . inputted in sequence are provided by shifting each of thefunction values by one clock while a clock position further delayed bytwo clocks is placed at the front.

The following will discuss an example in which two interpolation data B1and B2 are produced from one thinned-out data B based on such a datastructure. Here, b1 and b2 denote data on two lines, a center position bof the sampling data B processed by the digital basic function isinterposed between two lines of data, and a convoluting operation isperformed on the data b1 and b2. In this case, two adjacent data valuesb1 and b2 are expressed by the following equations.b1=A+8B−C   (8)b2=−A+8B+C   (9)

Based on the equations (8) and (9), the following equation isestablished.b1+b2=16B   (10)

This equation is transformed into the following equation.B=(b1/8+b2/8)/2   (11)

According to equation (11), the thinned-out data B corresponds to anintermediate value between two data of b1/8 and b2/8. Conversely, onethinned-out data B can be replaced with two interpolation data B1 and B2which are expressed by the following equations.B1=(A+8B−C)/8   (12)B2=(−A+8B+C)/8   (13)

Further, since the relationship indicated on the thinned-out data B byequation (11) is similarly established for other thinned-out data C, D,E, F, . . . , the following equations are established.C=(c1/8+c2/8)/2D=(d1/8+d2/8)/2E=(e1/8+e2/8)/2F=(f1/8+f2/8)/2

Therefore, as shown in the following equations, one thinned-out data Cis replaced with two interpolation data C1 and C2, one thinned-out dataD is replaced with two interpolation data D1 and D2, one thinned-outdata E is replaced with two interpolation data E1 and E2, and onethinned-out data F is replaced with two interpolation data F1 and F2.C→C1=(B+8C−D)/8, C2=(−B+8C+D)/8D→D1=(C+8D−E)/8, D2=(−C+8D+E)/8E→E1=(D+8E−F)/8, E2=(−D+8E+F)/8F→F1=(E+8F−G)/8, F2=(−E+8F+G)/8

As described above, when an interpolation value is obtained forthinned-out data (e.g., data B) on a sample point, a value obtained bymultiplying thinned-out data on the target sample point by 8 is added tovalues obtained by multiplying thinned-out data on sample points beforeand after the target sample point by +1 time and −1 time, and the addedvalue is divided by 8 to obtain a first interpolation value (e.g., B1).Further, a value obtained by multiplying thinned-out data on the targetsample point by 8 is added to values obtained by multiplying thinned-outdata on sample points before and after the target sample point by −1time and +1 time, and the added value is divided by 8 to obtain a secondinterpolation value (e.g., B2). The above operation is performed onthinned-out data on each sample point, so that the original thinned-outdata is oversampled twice.

Moreover, the same interpolation is performed based on the dataoversampled twice, so that the original thinned-out data can beoversamped to four times. Additionally, the same interpolation isperformed based on the interpolation data oversampled to four times, sothat the original thinned-out data can be oversampled to eight times.Theoretically, the same interpolation is repeated n times, so that theoriginal thinned-out data can be oversampled to 2^(n) times.

When the thinning-out operation is performed n times on the compressionpart to compress the original data to ½^(n) times, the interpolatingoperation is repeated n times on the decompression part, so thatinputted thinned-out data can be oversampled to 2^(n) times to reproducethe original data before compression.

Next, referring to FIG. 1, the following will discuss the configurationof a compressing device (thinning-out device) for realizing theabove-described thinning-out operation according to Embodiment 1.

In the compressing device of FIG. 1, circuits for performingthinning-out of 1/2 time are cascaded in three stages and the circuitconfigurations of the first to third stages are discriminated bynumerical subscripts (−1 to −3). Further, when the numerical subscriptsare different and the main symbols are the same, the circuitconfigurations have the same function.

A thinning-out circuit of the first stage operates on a clock 8 CK of areference frequency (e.g., 44.1 KHz). D-type flip-flops 1 ₋₁, 2 ₋₁, 3₋₁, and 4 ₋₁ of four stages delay sampling data (e.g., 16 bits), whichare inputted in sequence in a discrete manner, by one clock 8 CK of thereference frequency one by one. These D-type flip-flops 1 ₋₁ to 4 ₋₁correspond to delay circuits of four stages in claim 2.

An adder 5 ₋₁ adds data retrieved from the output taps of the D-typeflip-flops 2 ₋₁ and 3 ₋₁ of the second and third stages. An adder 6 ₋₁multiplies the output data from the adder 5 ₋₁ by 9. The adder 5 ₋₁ andthe adder 6 ₋₁ correspond to a first multiplying/adding circuitdescribed in claim 3.

An adder 7 ₋₁ adds data retrieved from the output taps of the D-typeflip-flops 1 ₋₁ and 4 ₋₁ of the first and fourth stages. A multiplier 8₋₁ multiplies the output data from the adder 7 ₋₁ by −1. The adder 7 ₋₁and the multiplier 8 ₋₁ correspond to a second multiplying/addingcircuit described in claim 3.

An adder 9 ₋₁ adds the output data from the two multipliers 6 ₋₁ and 8_(-1.) A multiplier 10 ₋₁ multiplies the output data from the adder 9 ₋₁by 1/16. The adder 9 ₋₁ and the multiplier 10 ₋₁ correspond to a thirdmultiplying/adding circuit described in claim 3.

To the above-described circuits, sampling data A, B, C, . . . , of FIG.3(a) are inputted in sequence, so that ½ thinned-out data expressed byequation (7) is outputted from the multiplier 10 ₁. The output data fromthe multiplier 10 ₋₁ is inputted to the D-type flip-flop 1 ₋₂ of athinning-out circuit in the second stage and ½ thinning processing isperformed in the second stage. The thinning-out circuit of the secondstage operates in the same manner as that of the first stage except thatthe thinning-out circuit operates on a clock 4 CK whose frequency ishalf the reference frequency.

Besides, according to FIG. 1, after thinned-out data (B+C)/2 of equation(7) is outputted from the multiplier 10 ₋₁, data (C+D)/2 is outputted.However, the data (C+D)/2 is ignored because the thinning-out circuit ofthe second stage operates on the clock 4 CK whose frequency is half thereference frequency, and the subsequent output data (D+E)/2 is processedas thinned-out data in the thinning-out circuit of the second stage.

The output data from the multiplier 10 ₋₂ provided in the final stage ofthe thinning-out circuit of the second stage is inputted to the D-typeflip-flop 1 ₋₃ in the thinning-out circuit of the third stage, and ½thinning-out processing is performed in the third stage. Thethinning-out circuit of the third stage operates in the same manner asthat of the first stage except for the thinning-out circuit operates ona clock 2 CK whose frequency is one fourth of the reference frequency.Data outputted from the thinning-out circuit of the third stage is heldby a D-type flip-flop 11 according to a clock CK whose frequency is oneeighth of the reference frequency, and then, the data is outputted asfinal thinning-out data (compressed data).

Next, referring to FIG. 2, the configuration of a decompressing device(interpolating device) for realizing the above-described interpolatingoperation according to Embodiment 1.

In the decompressing device of FIG. 2, circuits for performing doubleoversampling are cascaded in three stages and the circuit configurationsof the first to third stages are discriminated by numerical subscripts(−1 to −3). Further, when the numerical subscripts are different but themain symbols are the same, the circuit configurations have the samefunction.

An oversampling circuit of the first stage operates on a clock CK whosefrequency (5.5125 KHz) is one eighth of the reference frequency. D-typeflip-flops 21 ₋₁, 22 ₋₁, and 23 ₋₁ of three stages delay thinned-outdata one by one, which are inputted in sequence in a discrete manner, byone clock CK. These D-type flip-flops 21 ₋₁, 22 ₋₁, and 23 ₋₁ correspondto delay circuits of three stages in claim 52.

For example, data retrieved from the output tap of the D-type flip-flop21 ₋₁ forms the first terms of equations (12) and (13), data retrievedfrom the output tap of the D-type flip-flops 22 ₋₁ of the second stageforms the second term, and data retrieved from the output tap of theD-type flip-flops 23 ₋₁ of the third stage forms the third term.

The output data from the D-type flip-flops 21 ₋₁ of the first stage isinputted to one of the input terminals of an AND gate 25 ₋₁ via amultiplier 24 ₋₁ of −1 time (corresponding to a first multiplier ofclaim 53) and is inputted to one of the input terminals of an AND gate26 ₋₁ without passing through a multiplier (corresponding to +1 time).An inversion clock CK passing through an inverter 27 ₋₁ is inputted tothe other input terminal of the AND gate 25 ₋₁ is fed with. Further, theclock CK is inputted to the other input terminal of the AND gate 26 ₋₁.

The output data from the two AND gates 25 ₋₁ and 26 ₋₁ are outputted viaan OR gate 28 ₋₁. Thus, thinned-out data of +1 time is outputted fromthe OR gate 28 ₋₁ when the clock CK is “H”. Further, thinned-out data of−1 time is outputted from the OR gate 28 ₋₁ when the clock CK is “L”.Namely, the first term of equation (12) is obtained when the clock CK is“H”, and the first term of equation (13) is obtained when the clock CKis “L”. A first switching circuit of claim 53 is constituted by the twoAND gates 25 ₋₁ and 26 ₋₁, the inverter 27 ₋₁, and the OR gate 28 ₋₁.

The output data from the D-type flip-flop 22 ₋₁ of the second stage isoutputted via a multiplier 29 ₋₁ of +8 times (corresponding to a secondmultiplier of claim 53). As shown in equations (12) and (13), since the“±” sign of the second term is not changed in both of the equations,unlike the first term, a circuit for switching the sign based on theclock CK is not necessary.

The output data from the D-type flip-flops 23 ₋₁ of the third stage isinputted to one of the input terminals of an AND gate 31 ₋₁ via amultiplier 30 ₋₁ of −1 time (corresponding to a third multiplier ofclaim 53) and is inputted to one of the input terminals of an AND gate32 ₋₁ without passing through a multiplier (corresponding to +1 time).The clock CK is inputted to the other input terminal of the AND gate 31₋₁. Further, the inversion clock CK passing through an inverter 33 ₋₁ isinputted to the other input terminal of the AND gate 32 ₋₁.

The output data from the two AND gates 31 ₋₁ and 32 ₋₁ are outputted viaan OR gate 34 ₋₁. Thus, thinned-out data of −1 time is outputted fromthe OR gate 34 ₋₁ when the clock CK is “H”. Further, thinned-out data of+1 time is outputted from the OR gate 34 ₋₁ when the clock CK is “L”.Namely, the third term of equation (12) is obtained when the clock CK is“H”, and the third term of equation (13) is obtained when the clock CKis “L”. A second switching circuit of claim 53 is constituted by the twoAND gates 31 ₋₁ and 32 ₋₁, the inverter 33 ₋₁, and the OR gate 34 ₋₁.

The output data from the OR gate 28 ₋₁, the output data from theeight-times multiplier 29 ₋₁, and the output data from the OR gate 34 ₋₁are all added by two adders 35 ₋₁ and 36 ₋₁ (corresponding to an adderof claim 53). Thus, the arithmetic result of equation (12) is outputtedfrom the adder 36 ₋₁ when the clock CK is “H”, and the arithmetic resultof equation (13) is outputted from the adder 36 ₋₁ when the clock CK is“L”.

The thinned-out data A, B, C, . . . , of FIG. 3(b) are inputted insequence to the above-described circuit, so that interpolation data A,B1, B2, C1, C2, . . . , oversampled twice are outputted from the adder36 ₋₁. Besides, the data values are multiplied by ⅛ in equations (12)and (13). A circuit for the multiplication is provided in the finalstage of the oversampling circuit of the first stage.

In a data interpolating device of FIG. 2, for example, when twointerpolation data B1 and B2 are produced from one thinned data B, datais produced by using one eight-times multiplier 29 ₋₁ in common for thesecond term of equations (12) and (13) which are shared by theinterpolation data. In this way, the circuit shared for producing twointerpolation data is used in common as much as possible, therebysimplifying the entire circuit configuration.

An averaging circuit constituted by a D-type flip-flop 37 ₋₁, an adder38 ₋₁, and a 1/16-time multiplier 39 ₋₁ is provided in the output stageof the adder 36 ₋₁. Additionally, 1/8 time of the 1/16-time multiplier39 ₋₁ corresponds to 1/8 time of the equations (12) and (13) and theremaining 1/2 time constitutes a part of the averaging circuit.

The D-type flip-flop 37 ₋₁ delays the output data from the adder 36 ₋₁by one clock according to a clock 2 CK whose frequency is one fourth ofthe reference frequency. The adder 38 ₋₁ adds the output data from theadder 36 ₋₁ and the output data from the D-type flip-flop 37 ₋₁. The1/16-time multiplier 39 ₋₁ multiplies the output data from the adder 38₋₁ by 1/16 time.

The averaging circuit is provided for returning a relative position ofthe clock, which is shifted by the interpolation, to the originalposition. For example, when the interpolation data B1, B2, C1, C2, . . ., are outputted from the adder 36 ₋₁, the operations of (B1+B2)/2,(B2+C1)/2, (C1+C2)/2, . . . are performed in sequence in the averagingcircuit.

The results of the averaging operation will be expressed by thefollowing equations.(B1+B2)/2={{(A+8B−C)/8)+{(−A+8B+C)/8}}/2=B(B2+C1)/2={{(−A+8B+C)/8)+{(B+8C−D)/8}}/2=(−A+9B+9C−D)/16  (14)(C1+C2)/2={{(B+8C−D)/8)+{(−B+8C+D)/8}}/2=C

The shifted relative position of the clock is returned to the originalposition. Hence, as will be discussed later in FIG. 7, theabove-described averaging operation makes it possible to obtain apreferable frequency characteristic for the obtained sampling function.

The output data from the 1/16-time multiplier 39 ₋₁ is inputted to theD-type flip-flop 21 ₋₂ in the oversampling circuit of the second stage,and double oversampling is performed in the second stage. Theoversampling circuit of the second stage operates in the same manner asthat of the first stage except that the oversampling circuit operates ona clock 2 CK whose frequency is one fourth of the reference frequency.

The output data from a 1/16-time multiplier 39 ₋₂, which is provided inthe final stage of the oversampling circuit of the second stage, isinputted to the D-type flip-flop 21 ₋₃ in the oversampling circuit ofthe third stage and double oversampling is performed in the third stage.The oversampling circuit of the third stage operates in the same manneras that of the first stage except that the oversampling circuit operateson a clock 4 CK whose frequency is half the reference frequency.

FIG. 5 is a characteristic diagram showing oversampling results obtainedby inputting data of a unit pulse to the decompressing device of FIG. 2.In FIG. 5, <1> denotes input data of the unit pulse, <2> denotes doubleoversampling data, <3> denotes four-times oversampling data, and <4>denotes eight-times oversampling data. The waveform function of theoversampling data indicated by <4> can be differentiated once or moretimes over the whole range, and the waveform function is a samplingfunction of a finite base that converges to 0 on a finite samplingposition.

Therefore, when the data interpolation of the present embodiment isused, the sampling function of <4> in FIG. 5 is consequently used toperform superposition based on discrete thinned-out data, therebysmoothly interpolating values between thinned-out data by using thefunction differentiable once or more times.

In a conventional method of data interpolation of artificiallyincreasing a sampling frequency by an interpolating operation, asampling function referred to as a sinc function is normally used.

FIG. 6 is an explanatory view showing a sinc function. The sinc functionis obtained when Dirac delta function is subjected to inverse Fouriertransform. The sinc function is defined by sin(πft)/(πft) where fdenotes a sampling frequency. The sinc function has a value of 1 only onthe sample point of t=0 and has a value of 0 on other sample points.

In a method of data interpolation using such a sinc function, afterobtained interpolation values are held by a sample holding circuit toproduce a stepped signal waveform, a smooth signal is outputted bypassing the waveform through a low-pass filter. However, in this method,an outputted continuous signal is degraded in phase characteristic by alow-pass filter.

Further, since the above sinc function is a function converging to 0 at±8, when an accurate interpolation value is obtained, it is necessary tocalculate and add sinc function values corresponding to all the samplingdata values. However, in reality, because of the processing capability,the circuit size, and so on, a convoluting operation is performed whilethe range of sampling data to be considered is limited. For this reason,obtained interpolation values include a truncation error and an accurateinterpolation value cannot be obtained.

On the other hand, the sampling function of <4> in FIG. 5 is a functionof a finite base differentiable once or more times over the whole range.A sampling position along the lateral axis has a finite value other than0 only in a finite and local area and has a value of 0 in other areas.

Moreover, the sampling function of <4> in FIG. 5 is a function having amaximum value only on the central sample point and has a value of 0 onthe other several sample points. The function passes through all of thesample points required for obtaining a signal with a smooth waveform.

Therefore, instead of the conventional sinc function of FIG. 6, thesampling function of <4> in FIG. 5 is used to perform superpositionbased on thinned-out data, so that values between thinned-out data canbe smoothly interpolated by using a function differentiable once or moretimes. Hence, it is possible to eliminate the necessity for a low-passfilter and to prevent degradation of the phase characteristic.

Further, since the sampling function of <4> in FIG. 5 converges to 0 onthe finite sample point, only discrete data need to be considered withinthe finite range. Therefore, when a certain interpolation value iscalculated, it is necessary to consider only a limited number ofthinned-out data values, thereby significantly reducing the processingamount. Additionally, each thinned-out data out of the finite rangeoriginally needs to be essentially considered but is ignored in view ofthe processing amount and accuracy or the like. The truth is that suchthinned-out data does not need to be considered theoretically. Hence, itis also possible to prevent the occurrence of a truncation error.

Moreover, on the compression part, for example, when one thinned-outdata is obtained from two sampling data B and C, as expressed inequation (7), the thinned-out data is obtained by an operationconsidering sampling data A and D, which are adjacent to both sides ofthe target sampling data B and C, instead of a simple operation usingonly the target sampling data B and C. In this case, the operation isperformed based on a digital basic function serving as the original of asampling function causing no truncation error. Thus, at least whenthinned-out data is obtained as expressed in equation (7) inconsideration of the sampling data A and D adjacent to both sides of thesampling data B and C, it is possible to obtain thinned-out datarequired for faithfully reproducing original data on the decompressionpart.

FIG. 7 is a diagram showing a frequency characteristic of the samplingfunction of <4> in FIG. 5. As shown in FIG. 7, an extremely preferablefrequency characteristic is obtained. According to FIG. 7, a notchfilter enters right on a point where so-called return noise occurs,thereby effectively preventing the occurrence of return noise.

Besides, the decompressing device of FIG. 2 is an example of the circuitconfiguration for realizing the decompressing method of the presentinvention. The decompressing device is not limited to the above.

For example, the following circuits may be separately provided: a firstmultiplying/adding circuit for multiplying data retrieved from theoutput taps of the three D-type flip-flops by −1, 8, and +1 and addingthe data, and a second multiplying/adding circuit for multiplying dataretrieved from the output taps of the three D-type flip-flops by +1, 8,and −1 and adding the data.

FIG. 8 is a diagram showing an example of a circuit configuration ofthis case. Here, only a circuit for double oversampling is shown in FIG.8. As with FIG. 2, 2^(n)-times oversampling can be performed bycascading similar n circuits. Further, the averaging circuit is notshown in FIG. 8.

In FIG. 8, D-type flip-flops 41, 42, and 43 of three stages delaythinned-out data one by one, which are inputted in sequence in adiscrete manner, by one clock CK. A first multiplying/adding circuitcomprises a first multiplier 44 for multiplying the output data from theD-type flip-flop 41 in the first stage by −1, a second multiplier 45 formultiplying the output data from the D-type flip-flop 42 in the secondstage by 8, and adders 46 and 47 for adding output data from the firstmultiplier 44, the output data from the second multiplier 45, and theoutput data from the D-type flip-flop 43 of the third stage.

Moreover, a second multiplying/adding circuit comprises a thirdmultiplier 48 for multiplying the output data from the D-type flip-flop42 of the second stage by 8, a fourth multiplier 49 for multiplying theoutput data from the D-type flip-flop 43 of the third stage by −1, andadders 50 and 51 for adding the output data from the third multiplier48, the output data from the fourth multiplier 49, and the output datafrom the D-type flip-flop 41 of the first stage.

Data outputted from the first multiplying/adding circuit (adder 47) isinputted to one of the input terminals of an AND gate 52. An inversionclock CK passing through an inverter 53 is inputted to the other inputterminal of the AND gate 52. Further, data outputted from the secondmultiplying/adding circuit (adder 51) is inputted to one of the inputterminals of an AND gate 54. A clock CK is inputted to the other inputterminal of the AND gate 54.

The output data from the two AND gates 52 and 54 are outputted via an ORgate 55. Thus, the arithmetic result of equation (12) is outputted fromthe OR gate 55 when the clock CK is “H”, and the arithmetic result ofequation (13) is outputted from the OR gate 55 when the clock CK is “L”.

Further, instead of using the two eight-times multipliers in FIG. 8, oneeight-times multiplier may be shared as shown in FIG. 9. Additionally,although FIG. 9 shows only circuits for performing double oversampling,2^(n)-times oversampling can be performed by cascading n similarcircuits. Moreover, an averaging circuit is omitted in FIG. 9 as well.

A decompressing device shown in FIG. 9 comprises D-type flip-flops 61,62, and 63 of three stages for delaying thinned-out data one by one,which are inputted in sequence, by one clock CK. Further, thedecompressing device comprises a first multiplier 64 for multiplyingoutput data from the D-type flip-flop 61 of the first stage by −1, asecond multiplier 65 for multiplying output data from the D-typeflip-flop 62 of the second stage by 8, and a third multiplier 66 formultiplying output data from the D-type flip-flop 63 of the third stageby −1.

Moreover, the decompressing device comprises first adders 67 and 68 foradding the output data from the first multiplier 64, the output datafrom the second multiplier 65, and the output data from the D-typeflip-flop 63 of the third stage, and second adders 69 and 70 for addingthe output data from the second multiplier 65, the output data from thethird multiplier 66, and the output data from the D-type flip-flop 61 ofthe first stage.

Data outputted from the adder 68 is inputted to one of the inputterminals of an AND gate 71. An inversion clock CK passing through aninverter 72 is inputted to the other input terminal of the AND gate 71.Moreover, data outputted from the adder 70 is inputted to one of theinput terminals of an AND gate 73. A clock CK is inputted to the otherinput terminal of the AND gate 73.

Output data from the two AND gates 71 and 73 are outputted via an ORgate 74. Thus, the arithmetic result of equation (12) is outputted fromthe OR gate 74 when the clock CK is “H”, and the arithmetic result ofequation (13) is outputted from the OR gate 74 when the clock CK is “L”.

Besides, in the above embodiment, data is interpolated by performing theoperations of equations (12) and (13), and a shifted relative positionof the clock is corrected by further performing an averaging operationon obtained interpolation data. Meanwhile, the averaging operation maybe omitted by directly performing the operation of equation (14).

When the operation of equation (14) is directly performed, as tothinned-out data inputted in sequence, weighted addition according tothe value of a digital basic function is performed on thinned-out dataon two adjacent target sample points and thinned-out data on samplepoints which are adjacent to both sides of the target points, so thatinterpolation data for interpolating thinned-out data on the two samplepoints is obtained in sequence. For example, when the two targetthinned-out data are B and C, interpolation data (B+C)/2 between B and Cwill be calculated by the following equation.(B+C)/2=(−A+9B+9C−D)/16   (15)

FIG. 10 is a diagram showing an example of the circuit configuration ofthis case. Although only a circuit for performing double oversampling isshown in FIG. 10 as well, 2^(n)-times oversampling can be performed bycascading n similar circuits.

A decompressing device of FIG. 10 comprises D-type flip-flops 81, 82,83, and 84 of four stages for delaying thinned-out data, which areinputted in sequence, by one clock CK one by one. The D-type flip-flops81 to 84 of four stages correspond to delay circuits of four stages inclaim 59.

Further, the decompressing device comprises a first multiplier 85 formultiplying the output data from the D-type flip-flop 81 of the firststage by −1, a second multiplier 86 for multiplying the output data fromthe D-type flip-flop 82 of the second stage by 9, a third multiplier 87for multiplying the output data from the D-type flip-flop 83 of thethird stage by 9, and a fourth multiplier 88 for multiplying the outputdata from the D-type flip-flop 84 of the fourth stage by −1.Furthermore, the decompressing device comprises adders 89, 90, and 91for adding all the output data from the first to fourth multipliers 85to 88.

Data outputted from the adder 91 is inputted to one of the inputterminals of an AND gate 92. An inversion clock CK passing through aninverter 93 is inputted to the other input terminal of the AND gate 92.Moreover, thinned-out data inputted to the D-type flip-flop 81 of thefirst stage is inputted to one of the input terminals of an AND gate 95via a delay circuit 94 for making delay according to a delay of each ofthe circuit blocks 81 to 91. A clock CK is inputted to the other inputterminal of the AND gate 95.

The output data from the two AND gates 92 and 95 are outputted via an ORgate 96. Thus, when the clock CK is “H”, inputted thinned-out data isdirectly outputted from the OR gate 96. When the clock CK is “L”,interpolation data obtained by equation (15) is outputted from the ORgate 96.

Besides, FIG. 10 shows an example for performing the operation ofequation (15) and the configuration is not limited to that of FIG. 10.For example, instead of the multiplying/adding circuits 85 to 91 shownin FIG. 10, the following configuration may be used: amultiplying/adding circuit is constituted by a first adder for addingthe output data from the D-type flip-flop 81 of the first stage and theoutput data from the D-type flip-flop 84 of the fourth stage, a secondadder for adding the output data from the D-type flip-flop 82 of thesecond stage and the output data from the D-type flip-flop 83 of thethird stage, a first multiplier for multiplying the output data from thefirst adder by −1, a second multiplier for multiplying the output datafrom the second adder by 9, and a third adder for adding the output datafrom the first multiplier and the output data from the secondmultiplier. In this way, multipliers can be omitted.

As described above in detail, according to Embodiment 1, thinned-outdata is obtained on the compression part based on a digital basicfunction serving as the original of a sampling function of a finite basedifferentiable once or more times over the whole range, therebyachieving a compression ratio of at least 8. Further, interpolation datausing the same digital basic function is obtained on the compressionpart, so that the original data before compression can be reproducedwith substantial fidelity. The thinned-out data at this point can beobtained only by the quite simple four operations of equation (7) andinterpolation data can be obtained by the quite simple four operationsof equations (12) and (13) or equation (14).

According to these equations (7), (12), (13), and (14), when thinned-outdata and interpolation data are obtained for discrete data on a certainsample point, it is necessary to consider only discrete data on a targetsample point and discrete data on several sample points around thetarget point. Further, data to be compressed can be compressed anddecompressed as it is on a time base without performing time/frequencyconversion on the data, thereby simplifying the configuration withoutcomplicated operations.

Therefore, according to the present embodiment, it is possible toachieve shorter operation time as well as a higher compression ratio andhigher quality and to simplify the arithmetic circuit.

Moreover, in Embodiment 1, data values changed to −1, 1, 8, 8, −1 oneach clock were used as a digital basic function. Although the numericvalues are the best, other numeric values (e.g., a numeric value havinga weight of 1 or 0 instead of −1 on a part corresponding to both sides,a numeric value having a weight other than 8 on a part corresponding tothe center, etc.) is also applicable as a digital basic function.

Further, in Embodiment 1, the compressing device and the decompressingdevice are constituted by combining logic circuits like hardware. Thedevices may be constituted by a CPU or a computer system comprising anMPU, a ROM, and a RAM. The functions of the decompressing device and thecompressing device can be achieved also by operating programs stored inthe ROM and RAM.

Embodiment 2

The following will discuss Embodiment 2 of the present invention.Embodiment 2 employs a function obtained by shifting the function ofFIG. 4 by one clock and performing addition (averaging) thereon.

FIG. 11 is a diagram for explaining thinning-out and interpolatingprinciples of Embodiment 2. FIG. 11(a) shows the thinning-out principleand FIG. 11(b) shows the interpolating principle. First, referring toFIG. 11(a), the thinning-out principle of the present embodiment will bediscussed.

In the data structure of FIG. 11(a), the lateral axes of A, B, C, . . .denote sampling data on sample points that is inputted in sequence oneach clock and the data values are coefficients of a digital basicfunction. Further, the longitudinal axes of a, b, c, . . . denote centerpositions of sampling data processed by the digital basic function.

As shown in FIG. 11(a), the digital basic function for sampling data Ais provided by shifting each of the function values (−1, 0, 9, 16, 9, 0,−1) by one clock while the first clock position is placed at the front.Moreover, the digital basic function for the subsequent sampling data Bis provided by shifting each of the function values by one clock while aclock position after one clock from the first clock position is placedat the front. Similarly, the digital basic functions for sampling dataC, D, E, F, . . . inputted in sequence are provided by shifting each ofthe function values by one clock while a clock position further delayedby one clock is placed at the front.

In Embodiment 2, an operation for thinning out the sampling data A, B,C, . . . on the sample points to a half is performed based on such adata structure. Unlike Embodiment 1, the center position of the digitalbasic function is overlaid on one data position in Embodiment 2. Thus,successive sampling data is used alternately. As to the used samplepoint, a data value is replaced with a convoluted value on a line of thecenter position of a digital basic function corresponding to the samplepoint.

Namely, due to a lack of data required for operations, the firstsampling data A, B, and C remain in the same state without being thinnedout. As to the subsequent sampling data D, on a line of a centerposition d of the corresponding digital basic function, data values areadded and adjustment is made according to amplitude as expressed by thefollowing equation (16). The results are used as thinned-out data.D→(16D+9(C+E)−(A+G))/32   (16)

Further, the subsequent sampling data E is discarded and the subsequentsampling data F is used, and the sampling data F is replaced withthinned-out data obtained by the following equation (17) on a line of acenter position f of the corresponding digital basic function.F→(16F+9(E+G)−(C+I))/32   (17)

Similarly, convoluted values on every other clock positions h, j, l, . .. , are obtained as thinned-out data.

In this way, the same thinning-out operation is performed based on datathinned-out to a half, so that the original data can be thinned-out toone fourth. Moreover, the same thinning-out operation is performed basedon data thinned-out to one fourth, so that the original data can bethinned-out to one eighth. Theoretically, the original data can becompressed to ½^(n) by repeating the same thinning-out operation ntimes.

Referring to FIG. 11(b), the principle of data interpolation will bediscussed according to Embodiment 2. In the data structure of FIG.11(b), the lateral axes of A, B, C, . . . denote thinned-out datainputted in sequence on each clock and the data values are coefficientsof a digital basic function. Further, the longitudinal axes of a, b, c,. . . denote center positions of thinned-out data processed by thedigital basic function.

As shown in FIG. 11(b), the digital basic function for thinned-out dataA is provided by shifting each of the function values (−1, 0, 9, 16, 9,0, −1) by one clock while a clock position before two clocks from thefirst clock position is placed at the front. Further, the digital basicfunction for the subsequent thinned-out data B is provided by shiftingeach of the function values by one clock while the first clock positionis placed at the front. Similarly, the digital basic functions forthinned-out data C, D, E, F, . . . inputted in sequence are provided byshifting each of the function values by one clock while a clock positionfurther delayed by two clocks is placed at the front.

According to such a data structure, unlike Embodiment 1, the centerposition c of the digital basic function processed according to thevalue of the thinned-out data C is overlaid on one data position. Hence,in Embodiment 2, the data on the clock position c and data on clockpositions before and after the clock position c are used to perform aconvoluting operation, so that two interpolation data C1 and C2 areobtained from one thinned-out data C.

When data on three lines having the clock position c at the center aredenoted by c−, c, and c+ respectively, the data are expressed by thefollowing equations.c−=−A+9B+9C−D   (18)c=16C   (19)c+=−B+9C+9D−E   (20)

Based on the above equations (18) and (19), the following equation willbe established.(c−+c)=(−A+9B+25C−D)   (21)

Further, based on the above equations (19) and (20), the followingequation will be established.(c+c+)=(−B+25C+9D−E)   (22)

When adjusted amplitude is considered based on the equations (21) and(22), one thinned-out data C can be replaced with the two interpolationdata C1 and C2. C1 and C2 will be expressed by the following equations.C1=(−A+9B+25C−D)/32   (23)C2=(−B+25C+9D−E)/32   (24)

Moreover, the relationship expressed by equations (23) and (24)regarding the thinned-out data C is similarly established for the otherthinned-out data D, E, F, . . . Therefore, as shown in the followingequation, one thinned-out data D is replaced with two interpolation dataD1 and D2, one thinned-out data E is replaced with two interpolationdata E1 and E2, and one thinned-out data F is replaced with twointerpolation data F1 and F2.D→D1=(−B+9C+25D−E)/32, D2=(−C+25D+9E−F)/32E→E1=(−C+9D+25E−F)/32, E2=(−D+25E+9F−G)/32F→F1=(−D+9E+25F−G)/32, F2=(−E+25F+9G−H)/32. . . . . .

As described above, when an interpolating value is obtained forthinned-out data(e.g., data C) on a certain sample point, a valueobtained by multiplying thinned-out data on the target sample point by25, a value obtained by multiplying thinned-out data on a previoussample point by 9, a value obtained by multiplying thinned-out data twopoints before the sample point by −1, and a value obtained bymultiplying thinned-out data on the subsequent sample point by −1 areadded and the added value is divided by 32 to obtain a firstinterpolation value (e.g., C1).

Further, a value obtained by multiplying thinned-out data on the targetsample point by 25, a value obtained by multiplying thinned-out data onthe previous sample point by −1, a value obtained by multiplyingthinned-out data on the subsequent sample point by 9, and a valueobtained by multiplying thinned-out data two points after the samplepoint by −1 are added and the added value is divided by 32 to obtain asecond interpolation value (e.g., C2).

These operations are performed on each of the sample points, so that theoriginal data is oversampled twice.

The same interpolating operation is performed based on interpolationdata oversampled by twice, so that the original data can be oversampledto four times. Furthermore, the same interpolating operation isperformed based on interpolation data oversampled by four times, so thatthe original data can be oversampled to eight times. Theoretically, thesame interpolating operation is repeated n times, so that the originaldata can be oversampled to ½^(n) times.

FIG. 12 is a diagram showing an example of a configuration of acompressing device (thinning device) for realizing the above-describedthinning-out operation according to Embodiment 2.

In the compressing device of FIG. 12, circuits for performing athinning-out operation of 1/2 time are cascaded in three stages and thecircuit configurations of the first to third stages are discriminated bynumerical subscripts (−1 to −3). Further, when the numerical subscriptsare different and the main symbols are the same, the circuitconfigurations have the same function.

The thinning-out circuit in the first stage operates on a clock 8 CK ofa reference frequency (e.g., 44.1 KHz). D-type flip-flops 101 ₋₁, 102₋₁, 103 ₋₁, 104 ₋₁, 105 ₋₁, 106 ₋₁, and 107 ₋₁ of seven stages delaysampling data (e.g., 16 bits), which are inputted in sequence in adiscrete manner, by one clock 8 CK of the reference frequency one byone. These D-type flip-flops 101 ₋₁ to 107 ₋₁ correspond to delaycircuits of seven stages in claim 5.

An adder 108 ₋₁ adds data retrieved from the output taps of the D-typeflip-flops 101 ₋₁ and 107 ₋₁ in the first and seventh stages. Amultiplier 109 ₋₁ multiplies the output data from the adder 108 ₋₁ by−1. The adder 108 ₋₁ and the multiplier 109 ₋₁ correspond to a firstmultiplying/adding circuit in claim 6.

An adder 110 ₋₁ adds data retrieved from the output taps of the D-typeflip-flops 103 ₋₁ and 105 ₋₁ in the third and fifth stages. A multiplier111 ₋₁ multiplies the output data from the adder 110 ₋₁ by 9. The adder110 ₋₁ and the multiplier 111 ₋₁ correspond to a secondmultiplying/adding circuit in claim 6.

A multiplier 112 ₋₁ multiplies data retrieved from the output tap of theD-type flip-flop 104 in the fourth stage by 16.

Adders 113 ₋₁ and 114 ₋₁ add output data from the above threemultipliers 109 ₋₁, 111 ₋₁, and 112 ₋₁. A multiplier 115 ₋₁ multipliesthe output data from the adder 114 ₋₁ by 1/32. The adders 113 ₋₁, 114₋₁, and the multiplier 115 ₋₁ correspond to a third multiplying/addingcircuit described in claim 6.

To the above-described circuits, sampling data A, B, C, . . . , of FIG.11(a) are inputted one by one, so that 1/2 thinned-out data of equations(16) and (17) are outputted from the multiplier 115 ₋₁. The output datafrom the multiplier 115 ₋₁ is inputted to the D-type flip-flop 101 ₋₂ ofthe thinning-out circuit in the second stage and 1/2 thinning processingis performed in the second stage. The thinning-out circuit of the secondstage operates in the same manner as that of the first stage except thatthe circuit operates on a clock 4 CK whose frequency is half thereference frequency.

Besides, according to the circuits of FIG. 12, after thinned-out dataexpressed by equation (16) concerning the sampling data D is outputtedfrom the multiplier 115 ₋₁, thinned-out data of the sampling data E isoutputted. Thereafter, thinned-out data expressed by equation (17) ofthe sampling data F is outputted. However, the thinned-out data of thesampling data E is ignored because the thinning-out circuit of thesecond stage operates on the clock 4 CK whose frequency is half thereference frequency, and thinned-out data of the subsequent samplingdata F is processed in the thinning-out circuit of the second stage.

The output data from the multiplier 115 ₋₂ provided in the final stageof the thinning-out circuit in the second stage is inputted to theD-type flip-flop 101 ₋₃ of the thinning-out circuit in the third stage,and 1/2 thinning processing is performed in the third stage. Thethinning-out circuit of the third stage operates in the same manner asthat of the first stage except for the circuit operates on a clock 2 CKwhose frequency is one fourth of the reference frequency. Data outputtedfrom the thinning-out circuit of the third stage is held by the D-typeflip-flop 116 according to a clock CK whose frequency is one eighth ofthe reference frequency, and then, the data is outputted as finalthinning-out data (compression data).

FIG. 13 is a diagram showing an example of a configuration of adecompressing device (interpolating device) according to Embodiment 2.In the decompressing device of FIG. 13, circuits for performing doubleoversampling are cascaded in three stages and the circuit configurationsof the first to third stages are discriminated by numerical subscripts(−1 to −3). Further, when the numerical subscripts are different but themain symbols are the same, the circuit configurations have the samefunction.

An oversampling circuit of the first stage operates on a clock CK whosefrequency (5.5125 KHz) is one eighth of the reference frequency. D-typeflip-flops 121 ₋₁, 122 ₋₁, 123 ₋₁, 124 ₋₁, and 125 ₋₁ of five stagesdelay thinned-out data (e.g., 16 bits), which is inputted in sequence,by one clock CK one by one. These D-type flip-flops 121 ₋₁ to 125 ₋₁correspond to delay circuits of five stages in claim 63.

Data retrieved from the output tap of the D-type flip-flop 121 ₋₁ in thefirst stage is inputted to the multiplier 126 ₋₁ of −1 time. Dataretrieved from the output tap of the D-type flip-flop 122 ₋₁ in thesecond stage is inputted to the multiplier 127 ₋₁ of +9 times and amultiplier 133 ₋₁ of −1 time.

Data retrieved from the D-type flip-flop 123 ₋₁ in the third stage isinputted to a multiplier 128 ₋₁ of 25 times. Data retrieved from theoutput tap of the D-type flip-flop 124 ₋₁ in the forth stage is inputtedto a multiplier 129 ₋₁ of −1 time and a multiplier 134 ₋₁ of +9 times.Data retrieved from the output tap of the D-type flip-flop 125 ₋₁ in thefifth stage is inputted to a multiplier 135 ₋₁ of −1 time.

The output data from the multiplier 126 ₋₁ of −1 time, the multiplier127 ₋₁ of 9 times, the multiplier 128 ₋₁ of 25 times, and the multiplier129 ₋₁ of −1 time are all added by three adders 130 ₋₁, 131 ₋₁, and 132₋₁. The output data from the multiplier 133 ₋₁ of −1 time, themultiplier 128 ₋₁ of 25 times, the multiplier 134 ₋₁ of 9 times, and themultiplier 135 ₋₁ of −1 time are all added by three adders 136 ₋₁, 137₋₁, and 138 ₋₁.

Data outputted from the adder 132 ₋₁ is inputted to one of the inputterminals of an AND gate 139 ₋₁. A clock CK is inputted to the otherinput terminal of the AND gate 139 ₋₁. Further, data outputted from theadder 138 ₋₁ is inputted to one of the input terminals of the AND gate140 ₋₁. An inversion clock CK passing through an inverter 141 ₋₁ isinputted to the other input terminal of the AND gate 140 ₋₁.

The output data from the two AND gates 139 ₋₁ and 140 ₋₁ are supplied toa multiplier 143 ₋₁ of 1/32 time via an OR gate 142 ₋₁. Thus, thearithmetic result of equation (23) is outputted from the 1/32-timemultiplier 143 ₋₁ when the clock CK is “H”, and the arithmetic result ofequation (24) is outputted from the 1/32-time multiplier 143 ₋₁ when theclock CK is “L”.

The thinned-out data A, B, C, . . . , of FIG. 11(b) are inputted one byone to the above-described circuit, so that interpolation data A, B, C1,C2, D1, D2 . . . , oversampled twice are outputted from the 1/32 adder143 ₋₁.

The output data from the 1/32 -time multiplier 143 ₋₁ is inputted to theD-type flip-flop 121 ₋₂ of the oversampling circuit in the second stage,and double oversampling is performed in the second stage. Theoversampling circuit of the second stage operates in the same manner asthat of the first stage except that the circuit on a clock 2 CK whosefrequency is one fourth of the reference frequency.

The output data from the 1/32-time multiplier 143 ₋₂, which is providedin the final stage of the oversampling circuit in the second stage, isinputted to the D-type flip-flop 121 ₋₃ of the oversamping circuit inthe third stage, and double oversampling is performed in the thirdstage. The oversampling circuit of the third stage operates in the samemanner as that of the first stage except that the circuit operates on aclock 4 CK whose frequency is half the reference frequency.

The output data from a 1/32 -time multiplier 143 ₋₃, which is providedin the final stage of the oversampling circuit in the third stage, isheld by a D-type flip-flop 144 according to a clock 8 CK of thereference frequency, and then, the data is outputted as finalinterpolation data (decompression data).

In the case where the decompressing device is configured as FIG. 13, asampling function obtained by inputting data of a unit pulse issubstantially equal to that of <4> in FIG. 5. Therefore, when theinterpolating operation of Embodiment 2 is used, a value betweenthinned-out data can be smoothly interpolated using a functiondifferentiable once or more times. Hence, it is possible to eliminatethe necessity for a low-pass filter and to prevent degradation of thephase characteristic.

Further, when an interpolation value of one thinned-out data isobtained, it is necessary to consider only a limited number (four inequations (23) and (24)) of thinned-out data values, therebysignificantly reducing the processing amount. Additionally, thefollowing is not true: thinned-out data out of the finite rangeoriginally needs to be considered but is ignored in view of theprocessing amount and accuracy. The truth is that such thinned-out datadoes not need to be considered theoretically. Hence, it is also possibleto prevent the occurrence of a truncation error.

As described above in detail, like Embodiment 1, Embodiment 2 canachieve shorter operation time as well as both of a higher compressionratio and higher quality of reproduced data, and to simplify thearithmetic circuit.

Further, as shown in FIG. 11, a function obtained by shifting thefunction of FIG. 4 by one clock and performing addition (averaging) isused to obtain interpolation data in Embodiment 2. Thus, an averagingoperation has been already performed in the function. Therefore, it isnot necessary to perform any averaging operation after the interpolatingoperation of equations (23) and (24), thereby omitting an averagingcircuit.

Moreover, in Embodiment 2 as well, data values changed to −1, 1, 8, 8,1, −1 on each clock were used as a digital basic function. Although thenumeric value is the best, other numeric values (e.g., a numeric valuehaving a weight of 1 or 0 instead of −1 on a part corresponding to bothsides, a numeric value having a weight other than 8 on a partcorresponding to the center, etc.) is also applicable as a digital basicfunction.

In Embodiment 2 as well, the compressing device and the decompressingdevice are constituted by combining logic circuits like hardware. Thedevices may be constituted by a CPU or a computer system comprising anMPU, a ROM, and RAM. The functions of the decompressing device and thecompressing device can be achieved also by operating programs stored inthe ROM and RAM.

Embodiment 3

The following will discuss Embodiment 3 of the present invention.

FIG. 14 is a diagram showing an example of a configuration of acompressing device according to Embodiment 3. As shown in FIG. 14, thecompressing device of the present embodiment is constituted by a muteprocessing section 201, a thinning section 202, a linear compressingsection 203, a rounding section 204, and a blocking section 205.

The mute processing section 201 corresponds to replacing means of thepresent invention and rounds an absolute value of each sampling data,which is inputted as a target of compression, by a first predeterminedvalue (e.g., “4”). Further, when an absolute value of inputted samplingdata is smaller than the first predetermined value or when an absolutevalue of inputted sampling data is smaller than a second predeterminedvalue (e.g., “16”) and an average value in a short section ofdifferential data (the short section has a default value such as 8clocks) is smaller than a third predetermined value (e.g., “8”) thesampling data is regarded as being mute and is outputted after the datavalue is replaced with “0”.

With this operation, a DC offset is corrected to remove small noisecomponents included in inputted data and a compression ratio isimproved.

The thinning section 202 corresponds to thinning-out means of thepresent invention and performs any one of the thinning-out operationsdiscussed in Embodiment 1 and Embodiment 2 on sampling data outputtedfrom the mute processing section 201. One of the thinning-out operationsmay be selectively switched and used. A compression ratio of at least 8can be achieved by passing data to be compressed through thethinning-out section 202.

The linear compressing section 203 includes sampling point detectingmeans and compression data producing means of the present invention andperforms the following linear compression on thinned-out data outputtedfrom the thinning-out section 202. Namely, from sample points ofthinned-out data outputted from the thinning-out section 202, samplepoints are detected in sequence as sampling points. The sample point hasan error between a data value on a straight line connecting twothinned-out data and a thinned-out data value on the same sample pointas the data value on the straight line, the error being equal to orsmaller than a desired value. Then, a discrete amplitude data value isobtained on each of the detected sample points and a timing data valueindicative of a time interval between the sample points is obtained.

The following will discuss the detail of the operation for detecting thesampling points. Namely, from thinned-out data, reference thinned-outdata and another thinned-out data having a time interval within apredetermined range are selected. Then, from sample points each havingan error equal to or smaller than a desired value between a data valueon a straight line connecting the two thinned-out data and a thinned-outdata value on the same sample point as the data value on the straightline, a sample point having the longest time interval within thepredetermined range is detected as a sampling point.

FIG. 15 is a diagram for explaining the basic principle of linearcompression. In FIG. 15, a lateral axis denotes time and a longitudinalaxis denotes amplitude of thinned-out data. Reference numerals D1 to D9in FIGS. 15(a) and 15(b) each denote a part of thinned-out data inputtedto the linear compressing section 203 from the thinning-out section 202in a sampling period of one clock CK.

In the example of FIG. 15, thinned-out data D1 serves as referencethinned-out data which is used firstly. Further, a time interval is 6clocks at the maximum between two thinned-out data selected when asampling point is detected. Besides, when 3 bits or 4 bits are used as atiming data value, a time interval between thinned-out data may be 7clocks or 15 clocks at the maximum.

First, as shown in FIG. 15(a), the reference thinned-out data D1 andthinned-out data D7 having the largest time interval within thepredetermined range are selected. Then, it is judged whether errors areall equal to or smaller than the desired value between data values D2′,D3′, D4′, D5′, and D6′ on sample points on a straight line connectingthe two thinned-out data and thinned-out data values D2, D3, D4, D5, andD6 on the same sample points as the data values D2′ to D6′ on thestraight line.

Namely, it is judged whether errors between the data values D2′, D3′,D4′, D5′, and D6′ on the straight line connecting the two thinned-outdata D1 and D7 and the thinned-out data values D2, D3, D4, D5, and D6are all within the range of desired values indicated by dotted lines.When this condition is satisfied, the sample point of the thinned-outdata D7 is detected as a sampling point. However, in this example, sincean error between the data value D4′ on the straight line and thecorresponding thinned-out data value D4 exceeds the desired value, theoperation proceeds without using any sample point of the thinned-outdata D7 as a sampling point at this point.

Next, as shown in FIG. 15(b), the thinned-out data D6 is selected. Thethinned-out data D6 has a time interval from the reference thinned-outdata D1 that is shorter than that of the data D7 by one clock CK. Then,it is judged whether errors are all equal to or smaller than the desiredvalue between data values D2″, D3″, D4″, and D5″ on sample points on astraight line connecting two thinned-out data D1 and D6 and thinned-outdata values D2, D3, D4, and D5 on the same sample points as the datavalues D2″ to D5″ on the straight line.

When all the errors are equal to or smaller than the desired value, thesample point of the thinned-out data D6 is detected as a sampling point.In this example, since errors between the data values D2″, D3″, D4″, andD5″ and the thinned-out data values D2, D3, D4, and D5 are all equal toor smaller than the desired value, the sample point of the thinned-outdata D6 is detected as a sampling point.

Additionally, when any of the straight lines connecting between D1 andD7, between D1 and D6, . . . , between D1 and D3 does not satisfy such acondition that all the errors are equal to or smaller than the desiredvalue, the sample point of the thinned-out data D2 is detected as asampling point. Namely, since another thinned-out data does not existbetween the thinned-out data D1 and D2, this section does not requireany above error operation. Hence, when any of straight lines connectingthe other sections does not satisfy the error condition, the position ofthe thinned-out data D2, which is adjacent to the thinned-out data D1currently serving as the reference data, is detected as a samplingpoint.

After one sampling point is detected, the data on the sampling point isnewly used as reference thinned-out data and the same operation isperformed therefrom within a range of 6 clocks. Thus, all the errors areequal to or smaller than the desired value from the thinned-out data D6within the range of 6 clocks, and a sample point having the longest timeinterval from the thinned-out data D6 is detected as the subsequentsampling point.

A plurality of sampling points are similarly detected in sequence. Then,the following data values are obtained in pairs: discrete amplitude datavalues on the detected sampling points and timing data values indicatingthe time intervals between the sampling points by the number of clocks.In the above example, pairs (D1, 5), (D6, *), . . . of amplitude datavalues (D1, D6, . . . ) and timing data values (5, *, . . . ) areobtained.

The above explanation discussed an example where sample points (samplepoints of the thinned-out data D1 and D7) having the maximum timeinterval between two thinned-out data within the predetermined range arefirstly selected to start error decision and the operation is performedso as to shorten the time intervals in sequence. The method of detectingsampling points is not limited to the above.

For example, sample points (sample points of the thinned-out data D1 andD3) having the minimum time interval between two thinned-out data withinthe predetermined range may be firstly selected to start error decisionand the operation may be performed so as to increase the time intervalsin sequence. Further, sample points (e.g., sample points of thethinned-out data D1 and D4) having a time interval between twothinned-out data around the center within the predetermined range may beselected to start error decision. Furthermore, error decision may beperformed on all the patterns of available time intervals within thepredetermined range, and then, a pattern having the longest timeinterval may be selected from the patterns satisfying the errorcondition.

In some cases, two or more sample points satisfying the error conditionexist within the predetermined range from the reference thinned-outdata. In this case, a sample point having the longest time interval fromthe reference thinned-out data is detected as a sampling point from thetwo or more sample points satisfying the error condition. Hence, a valueof each timing data can be within the predetermined range of bits and tominimize the number of detected sampling points, thereby increasing acompression ratio accordingly.

Referring to FIG. 16, the following will discuss the method ofcalculating an error between a data value on a straight line connectingtwo thinned-out data and a thinned-out data value on the same samplepoint as the data value. FIG. 16(a) is a diagram showing an error e2when a straight line connects the reference thinned-out data D1 and thethinned-out data D3 which is two clocks away from the data D1.

In FIG. 16(a), the error e2 between the thinned-out data D2 between thedata D1 and D3 and data D2′ on the straight line connecting the data D1and D3 is expressed by the following equation (25).e2=(D2−D1)−(D3−D1)/22e2=2D2−2D1−D3+D1=2D2−D1−D3=(D2D1)−(D3−D2)=D2′−D3′e2=−(D3′−D2′)/2=−D3″/2   (25)

In equation (25), a sign ′ denotes a first differential value and ″denotes a second differential value. As shown in equation (25), when thestraight line has a time interval of 2 clocks, the error e2 can beexpressed by a double differential value of the thinned-out data D3.Hence, when an allowable error is δ, in the linear compressing section203 of FIG. 14, it is judged whether the decision condition of |e2↑≦δ issatisfied or not. In this equation, a sign | | denotes an absolutevalue.

FIG. 16(b) is a diagram showing two errors e2 and e3 when a straightline connects the reference thinned-out data D1 and the thinned-out dataD4 which is three clocks away from the data D1. In FIG. 16(b), theerrors e2 and e3 between the thinned-out data D2 and D3 and data D2″ andD3″ on the straight line connecting the data D1 and D4 are expressed bythe following equations (26) and (27).e2=(D2−D1)−(D4−D1)/33e2=3D2−3D1−D4+D1=3D2−2D1−D4=2(D2−D1)−(D4−D2)=2(D2−D1)−(D4−D3)−(D3−D2)=2D2′−D4′−D3′=−(D4′−D3′)−2(D3′−D2′)=−D4″−2D3″e2=−1/3 (D4″+2D3″)   (26)e3=(D3−D1)−2(D4−D1)/33e3=3D3−3D1−2D4+2D1=3D3−D1−2D4=−2(D4−D3)+D3−D1=−2(D4−D3)+(D3−D2)+(D2−D1)=−2D4′+D3′+D2′=−2(D′4−D3′)−(D3′−D 2′)=−2D4′−D3″e3=1/3 (2D4′+D3′)   (27)

As shown in equations (26) and (27), when the straight line has a timeinterval of 3 clocks, the errors e2 and e3 can be expressed by usingdouble differential values of the sampling data D3 and D4. In this case,the linear compressing section 203 judges whether the decisionconditions of |e2|≦δ and |e3|≦δ are satisfied or not. Additionally, thefollowing operation is also applicable: it is firstly judged which islarger between the errors e2 and e3, and only the larger one is used tojudge whether the judging conditions are satisfied or not.

Similarly, when the straight line has a time interval of 4 clocks,errors e2, e3, and e4 can be expressed by the following equations (28)to (30) using double differential values of the thinned-out data D3, D4,and D5.e2=−1/4(D5″+2D4″+3D3″)   (28)e3=−1/4(2D5″+D4″+2D3″)   (29)e4=−1/4(3D5″+2D4″+D3″)   (30)

In this case, in the linear compressing section 203 of FIG. 14, it isjudged whether the decision conditions of |e2|≦δ, |e3|≦δ, and |e4|≦δ aresatisfied or not. The following operation is also applicable: it isfirstly judged which is the largest among the errors e2, e3, and e4, andonly the largest one is used to judge whether the decision conditionsare satisfied or not.

Similarly, when the straight line has a time interval of 5 clocks,errors e2, e3, e4, and e5 can be expressed by the following equations(31) to (34) using double differential values of sampling data D3, D4,D5, and D6.−e2=1/5(D6″+2D5″+3D4″+4D3″)   (31)−e3=1/5(2D6″+4D5″+6D4″+3D3″)   (32)−e4=1/5(3D6″+6D5″+4D4″+2D3″)   (33)−e5=1/5(4D6″+3D5″+2D4″+D3″)   (34)

In this case, in the linear compressing section 203 of FIG. 14, it isjudged whether the decision conditions of |e2|≦δ, |e3|≦δ, |e4|≦δ, and|e5|≦δ are satisfied or not. The following operation is also applicable:it is firstly judged which is the largest among the errors e2, e3, e4,and e5 and only the largest one is used to judge whether the decisionconditions are satisfied or not.

Similarly, when the straight line has a time interval of 6 clocks,errors e2, e3, e4, e5, and e6 can be expressed by the followingequations (35) to (39) using double differential values of sampling dataD3, D4, D5, D6, and D7.e2=−1/6(D7″+2D6″+3D5″+4D4″+5D3″)   (35)e3=−1/6(2D7″+4D6″+6D5″+8D4″+4D3″)   (36)e4=−1/6(3D7″+6D6″+9D5″+6D4″+3D3″)   (37)e5=−1/6(4D7″+8d6″+6D5″+4D4″+2D3″)   (38)e6=−1/6(5D7″+4D6″+3D5″+2D4″+D3″)   (39)

In this case, in the linear compressing section 203 of FIG. 14, it isjudged whether the decision conditions of |e2|≦δ, |e3|≦δ, |e4|≦δ,|e5|≦δ, and |e6|≦δ are satisfied or not. The following operation is alsoapplicable: it is firstly judged which is the largest among the errorse2, e3, e4, e5, and e6 and only the largest one is used to judge whetherthe decision conditions are satisfied or not.

As shown in equations (25) to (39), the error data used for the linearcompression of the present embodiment can be all obtained using only thedouble differential values of the thinned-out data. Then, the linearcompressing section 203 obtains error data from the double differentialvalues of the thinned-out data and detects sample points satisfying theerror conditions as sampling points. Subsequently, the linearcompressing section 203 outputs amplitude data of the detected samplingpoints and timing data indicative of time intervals between the samplingpoints.

Further, the rounding section 204 corresponds to rounding means of thepresent invention and rounds lower-order bits of amplitude dataoutputted from the linear compressing section 203. The roundingoperation can be performed by, for example, dividing output data fromthe linear compressing section 203 by a predetermined value (e.g., 256or 512). Such a rounding operation can reduce a data length by severalbits per word, thereby significantly reducing the data amount.

Amplitude data inputted to the rounding section 204 is, for example,signed data of 16 bits which can express a large data value up to 32767.However, in the case of voice data of audible tone, actually used datahas a relatively large value in many cases and thus data hardly appearsin a relatively small data area of the entire data area (0 to 32767)expressed by 16 bits. Therefore, even when lower-order bits are cut fromdata having such a large value, the quality of reproduced voice ishardly affected.

Moreover, as a rounding operation, instead of simply performing divisionas described above by using a predetermined value, a data value may berounded so that the input data and output data from the rounding section204 have a non-linear relationship. FIG. 17 is a diagram showing anexample of the rounding operation of this case. In the example of FIG.17, a logarithm of a data value inputted from the linear compressingsection 203 is calculated and the value is used as the output data fromthe rounding section 204.

Further, the following operation is also applicable: as shown in FIG.18, the logarithmic curve of FIG. 17 is approximated by combiningseveral lines. The approximate function may be used to change theamplitude of outputted data according to amplitude of data inputted fromthe linear compressing section 203, so that an input data value and anoutput data value have a non-linear relationship. Additionally, in theexample of FIG. 18, the logarithmic curve of FIG. 17 is approximated bycombining five lines. The accuracy can be further improved by combiningmore than five lines.

The rounding operation is performed according to such a non-linearfunction, so that output data values can be concentrated on a centraldata area where most data appears in the entire data area of voice dataof audible tone expressed by 16 bits. Thus, it is possible to reduce theinfluence of the rounding operation and lower quantization noise in anarea having small amplitude, thereby further reducing the influence ofthe rounding operation on the quality of reproduced voice.

Additionally, when the logarithmic function is used to perform therounding operation as shown in FIG. 17, reproduced voice somewhatchanges in quality according to a bottom value of the logarithm. Thebottom value of the logarithm may be set arbitrarily as a parameter. Acompression ratio and the quality of reproduced voice are affecteddepending upon how to handle a value after the decimal point of a datavalue which is changed to a logarithm. Hence, it may be arbitrarily setas a parameter whether a data value after the decimal point should bedropped to place emphasis on a compression ratio and how many digits ofthe data value should be used after the decimal point to place emphasison the quality of reproduced voice.

Besides, in the example of FIG. 14, amplitude data on a sampling pointis extracted first and the rounding operation is performed on theextracted amplitude data. Conversely, the following operation is alsoapplicable: the rounding operation is performed first on all data afterthe mute processing or all thinned-out data after the thinning-outoperation, and amplitude data on sampling points are extracted from therounded amplitude data.

Next, the blocking section 205 of FIG. 14 adds header information toamplitude data, in which lower-order bits are rounded by the roundingsection 204, and timing data produced by the linear compressing section203 and properly performs blocking thereon, and the blocking section 205outputs the data as compression data. The outputted compression data istransmitted to a transmission path or recorded in a recording medium.

FIG. 19 is a diagram showing an example of a configuration of adecompressing device according to Embodiment 3 for the compressingdevice configured as FIG. 14. As shown in FIG. 19, the decompressingdevice of the present embodiment is constituted by an inverse blockingsection 211, an inverse rounding section 212, a linear decompressingsection 213, and an interpolating section 214.

The inverse blocking section 211 extracts amplitude data and timing datafrom compression data based on header information included in theblocked compression data. The inverse rounding section 212 correspondsto inverse rounding means of the present invention and perform aninverse rounding operation on amplitude data extracted from the inverseblocking section 211. The inverse rounding operation is contrary to therounding section 204 on the compression part.

Namely, when a data value is simply divided by a predetermined valuesuch as 256 and 512 in the rounding section 204 of FIG. 14, the inverserounding section 212 multiplies amplitude data by 256 or 512. Further,when the rounding section 204 performs a non-linear rounding operationusing the logarithm or the approximate function of FIGS. 17 and 18, anon-linear inverse rounding operation is performed using the exponentialfunction or the approximate function of FIGS. 20 and 21 that arereversed from the above functions.

Additionally, when the exponential function of FIG. 20 is used toperform an inverse rounding operation, a value of the exponent may bearbitrarily set as a parameter. Moreover, it may be set arbitrarily as aparameter whether a data value after the decimal point should be droppedand how many digits of the data value should be used after the decimalpoint. In this case, the fractional portion is dropped duringcompression and a data value after the decimal point is used duringdecompression, so that the quality of reproduced voice can be improvedwith a higher compression ratio.

The linear decompressing section 213 corresponds to first interpolatingmeans of the present invention and sequetially performs interpolatingoperations for linearly interpolating amplitude data on successivesampling points by using amplitude data outputted from the inverserounding section 212 and timing data outputted from the inverse blockingsection 211, so that interpolation data for interpolating amplitude datavalues is produced.

Namely, the linear decompressing section 213 inputs timing data includedin compression data from the inverse blocking section 211 and produces areading clock from an input clock CK. The reading clock indicatesirregular time intervals equal to sampling points detected on thecompression part. Then, according to the generated reading clock,amplitude data after the inverse rounding operation are inputted in twosfrom the inverse rounding section 212, and an operation is performed forinterpolating the two amplitude data by a straight line, so thatinterpolation data between the sampling points is produced.

In this way, the linear decompression just linearly interpolatesamplitude data on the sampling points, on which the inverse roundingoperation is performed, at time intervals indicated by timing data.During the compression of the present embodiment, when linearinterpolation is performed between two thinned-out data, an error madeby another thinned-out data between the two thinned-out data from theinterpolated straight line is observed, and a point not having a largeerror even after the linear interpolation is detected as a samplingpoint. Therefore, by simply performing linear interpolation betweenamplitude data on the sampling points obtained thus, it is possible toreproduce data with a waveform substantially identical with that of theoriginal thinned-out data.

The interpolating section 214 corresponds to second interpolating meansof the present invention and performs one of the interpolatingoperations discussed in Embodiment 1 and Embodiment 2 on discrete firstinterpolation data outputted from the linear decompressing section 213,so that second interpolation data is produced. Any of the interpolatingoperations may be selectively switched and used. Digital interpolationdata produced thus is converted to an analog signal by a D/A convertingsection (not shown) and the signal is outputted as a reproduced analogsignal when necessary.

The compressing device and the decompressing device configured accordingto the present embodiment are constituted by a CPU or a computer systemcomprising an MPU, a ROM, and a RAM, and the functions of the devicescan be achieved by operating programs stored in the ROM and the RAM.

Moreover, the compressing device and the decompressing device configuredthus according to the present embodiment may be constituted by combininglogic circuits like hardware.

FIG. 22 is a waveform chart for comparing the original data beforecompression and reproduced data obtained by decompression whenEmbodiment 3 is adopted. As shown in FIG. 22, the waveform of theoriginal data and the waveform of the reproduced data are substantiallyidentical with each other and FIG. 22 looks as if only one waveformexisted.

FIG. 23 is a diagram showing the input/output characteristics of theoriginal data before compression and reproduced data obtained bydecompression. As shown in FIG. 23, extremely preferable input/outputcharacteristics are obtained and the original data and reproduced dataare substantially identical with each other.

FIG. 24 is a chart showing the frequency characteristics ofdecompression data obtained by inputting one compression data producedby the compressing device of FIG. 14 into the decompressing device shownin FIG. 19. As shown in FIG. 24, extremely preferable frequencycharacteristics are obtained. According to FIG. 24, a notch filterenters right on a part where so-called return noise occurs, therebyeffectively reducing the occurrence of return noise.

As discussed above in detail, according to Embodiment 3, thinned-outdata is obtained in the thinning section 202 on the compression partbased on a digital basic function serving as the original of a samplingfunction of a finite base differentiable once or more times over thewhole range, thereby achieving a compression ratio of 8.

Furthermore, in the linear compressing section 203, only data on asampling point satisfying the error condition is extracted fromthinned-out data obtained by the thinning section 202, and only pairs ofthe data and timing data are obtained. Moreover, in the rounding section204, since an operation is performed for rounding lower-order bits ofamplitude data retrieved from the linear compressing section 203, it ispossible to reduce a data length by several bits per word and thusachieve a substantial reduction in data amount.

As is apparent from the above description, the present embodiment canentirely achieve an extremely high compression ratio (about eight toseveral hundreds).

In addition, the interpolating section 214 on the decompression partobtains interpolation data by using the same function as the digitalbasic function used by the thinning section 202 on the compression part,so that the original data before compression can be reproduced withsubstantial fidelity. Further, the linear compressing section 203corresponding to the linear decompressing section 213 detects a samplepoint as a sampling point, on which an error from the original data doesnot exceed a desired value even when linear interpolation is performedduring decompression, and thus preferred reproducibility to the originaldata can be achieved.

Particularly, regarding interpolation data produced between samplingpoints by linear interpolation, it is possible to achieve an extremelysmall phase shift as well as a small amplitude error as compared withthe original data before compression. When voice is used as data to becompressed, the phase shift is considerably affected by timbre. However,since phase shift hardly appears in the present embodiment, the timbreof the original data can be reproduced with fidelity.

Further, regarding the rounding operation is performed on thecompression part, most amplitude data to be rounded appear in a dataarea around the center of the whole data area and few amplitude dataappear in a data area around the ends. Thus, even it lower-order bitsare reduced, it is possible to eliminate the influence on the quality ofreproduced data on the decompression part.

Additionally, in the present embodiment, the rounding operation isperformed so that a data value before the rounding operation and a datavalue after the rounding operation have a non-linear relationship.Hence, when voice is used as data to be compressed, in the whole dataarea indicating voice data of audible tone, output data values areconcentrated on a data area around the center where most data appear. Itis possible to reduce the influence of the rounding operation and tofurther reduce the influence on the quality of reproduced voice on thedecompression part.

Further, the present embodiment makes it possible to compress anddecompress data to be compressed as it is on a time base withoutperforming any time/frequency conversion. In addition, the thinning-outoperation and the corresponding interpolating operation can be performedby extremely simple four operations, and the linear compression and thecorresponding linear decompression can be performed only by performing alinear interpolating operation which is particularly simple amonginterpolating operations.

Therefore, the entire operations are not complicated at higher speed andthe configuration can be simplified. When compression data istransmitted from the compression part and is reproduced on thedecompression part, inputted compression data can be sequentiallyprocessed and reproduced by extremely simple linear interpolatingoperations on a time base, thereby achieving a real-time operation.

As described above, the present embodiment makes it possible to achievea higher compression ratio while maintaining extremely preferablequality of reproduced data. In addition, the operation time can beshortened and the arithmetic circuit can be simplified.

Further, in Embodiment 3, interpolation data between amplitude data onsampling points is obtained by linear interpolation on the decompressionpart. The interpolating operation is not limited to this example. Forexample, interpolation data may be obtained by curve interpolation usinga predetermined sampling function. Moreover, it is also possible toperform an interpolating operation described in Japanese PatentApplication No. 11-173245 and so on applied before by the applicant. Inthis case, since a waveform extremely close to an analog waveform can beobtained by interpolation itself, it is also possible to eliminate thenecessity for a D/A converter and an LPF in the subsequent stage of theinterpolating operation.

Besides, the following operation is also applicable: curve interpolationis used on the compression part as well as the decompression part, andas sampling points, sample points are sequentially detected where anerror from the original data is equal to or smaller than a desired valuewhen curve interpolation is performed between two thinned-out dataincluded in data to be compressed. In this case, it is preferable thatthe curve interpolation is the same as that of the decompression part.

Further, in Embodiment 3, the number of bits of timing data is 3 bitsand error decision is performed by drawing a straight line within arange of 6 clocks from the reference thinned-out data. The presentinvention is not limited to this example. For example, a predeterminedrange for error decision may be set at 7 clocks. Moreover, the number ofbits of timing data may be 4 or more bits, and the predetermined rangefor error decision by drawing a straight line from the referencethinned-out data may be 8 clocks or more. Thus, a compression ratio canbe further improved. Additionally, the number of bits of the timing dataor the predetermined range for error decision may be arbitrarily set asa parameter.

Moreover, in Embodiment 3, successive values are applicable as timeintervals between two thinned-out data which are used for error decisionfor detecting sampling points. For example, when error decision isperformed within a range of 16 clocks at the maximum (the number of bitsin timing data is 5 bits), timing data values applicable as timeintervals from the reference thinned-out data are included in any of 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16.

Meanwhile, timing data values applicable as time intervals may bediscontinuous within a range wider than a predetermined interval. Forexample, when error decision is performed within a range of 16 clocks atthe maximum, timing data values applicable as time intervals from thereference thinned-out data may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14,16, 18, 20, 24 and so on.

In this case, without increasing the number of error decisions fordetecting one sampling point, it is possible to increase a maximum rangeapplicable as time intervals between two thinned-out data. Hence, on apart where the fluctuations in amplitude are not so large, for example,on a mute part, it is possible to maximize an interval between samplingpoints to minimize the number of sampling points without causing anydelay in decision time, thereby further improving a compression ratio.

Further, time intervals between two thinned-out data are continuouswithin a range narrower than a predetermined interval (a range wheretime intervals are “10” or less). Thus, error decision can be performedmore accurately on this part. Normally, a time interval from thereference sample point to a sample point, on which an error exceeds adesired value, frequently appears in a narrower range than thepredetermined interval. When applicable time intervals are made discretein a range where the error condition is satisfied in many cases, it isconsidered that the number of sampling points increases in reverse.

For example, when timing data values applicable as time intervals fromthe reference thinned-out data are set at 2, 4, 6, . . . , even if themaximum time interval for satisfying the error condition is originally 5clocks, error decision is not performed on the 5 clocks. Thus, anactually used time interval is 4 clocks. When such a state occursfrequently, the number of detected sampling points increasesaccordingly. However, the number of detected sampling points can beminimized by providing successive time intervals which are applicable ina narrower range than the predetermined interval.

Further, in Embodiment 3, the error decision for detecting samplingpoints is performed restrictedly within a range from the referencesample point to a predetermined clock. The present invention is notlimited to this example. For example, an operation is performed withoutlimiting within a predetermined range a time interval between two dataselected for detecting discrete sampling points. Then, sample pointsjust before sample points having errors exceeding a desired value may besequentially detected as sampling points. In this case, it is possibleto maximize an interval between the sampling points and to furtherreduce the number of detected sampling points, thereby achieving ahigher compression ratio.

Additionally, as an allowable value of an error that is used inEmbodiment 3, a value such as, for example, 256, 384, and 512 can beused. An allowable value is not limited to these numeric values. When anallowable value of an error is reduced, it is possible to achievecompression and decompression placing emphasis on reproducibility of areproduced analog signal. Further, when an allowable value of an erroris increased, it is possible to achieve compression and decompressionplacing emphasis on a compression ratio. An allowable value of an errormay be arbitrarily set as a parameter.

Moreover, the following operation is also applicable: an error allowablevalue is used as a function, an error allowable value is increased, forexample, on a part having greater amplitude, and an error allowablevalue is reduced on a part having lesser amplitude. On a part havinggreater amplitude, even a somewhat large error does not stand out anddoes not seriously affect the sound quality. Therefore, when such anerror allowable value is dynamically changed as a function of dataamplitude, it is possible to maximize an interval between samplingpoints to minimize the number of detected sampling points on a partwhere even a somewhat large error does not stand out, and it is possibleto prevent an error from increasing on a part where the error relativelystands out. Hence, it is possible to further improve a compression ratiowhile maintaining the extremely preferable sound quality of reproduceddata.

Besides, the following operation is also applicable: an error allowablevalue is used as a function of a frequency, an error allowable value isincreased, for example, on a part having a high frequency, and an errorallowable value is reduced on a part having a low frequency. On ahigh-frequency part on signals inputted in series as a target ofcompression, that is, on a part having relatively large fluctuations insampling data value even on a close sample point, the number of detectedsampling points increases when an error allowable value is small, andthus a high compression ratio may not be achieved. However, bydynamically increasing an error allowable value on the high-frequencypart, a compression ratio can be further improved while entirelymaintaining the preferable sound quality of reproduced data.

As a matter of course, an error allowable value may be dynamicallychanged as a function for both of data amplitude and a frequency.

Moreover, in Embodiment 3, when the rounding operation is performed in anon-linear manner, data values before and after the rounding operationhave a relationship of a logarithmic function. As long as therelationship placing emphasis on some of data areas, a function otherthan the logarithmic function can be used.

Besides, in the configuration of the compressing device shown in FIG.14, the mute processing section 201 can be omitted.

Further, the rounding section 204 may be omitted for compression ofimage data.

Embodiment 4

The following will discuss Embodiment 4 of the present invention.

FIG. 25 is a diagram showing an example of a configuration of acompressing device according to Embodiment 4. In FIG. 25, members havingthe same reference numerals as those of FIG. 14 have the same functionsand the overlapping explanation is omitted.

As shown in FIG. 25, the compressing device of the present embodiment isconstituted by a format converting section 301, a mute processingsection 201, a thinning section 202, a rounding section 204, a zerocompressing section 302, and a blocking section 303.

The format converting section 301 converts the format of an input signalto a format suitable for the compressing device of the presentembodiment. For example, an inputted signal of WAV (wave) format isconverted to a signal of TXT (text) format. When the input signal is ananalog signal, the format is converted after the analog signal undergoesA/D conversion.

The zero compressing section 302 corresponds to zero compressing meansof the present invention. When zero data continues over n clocks or morein output data from the rounding section 204, the zero compressingsection 302 replaces n or more successive zero data with a pair of−0(H80) and the number of clocks of the successive zero data and outputsthe pair. An output value reaches up to 255 when a rounding operation isperformed using a logarithmic function in the rounding section 204.Since −0(H80) does not exit as a data value, this value can be used as astart mark of zero compression.

When recovery is made from zero compression, it is detected that datahaving a predetermined threshold value or more continues over m clocks(e.g., 2 clocks) or more, and recovery is made from the zero compressionto return to a normal operation.

The blocking section 303 adds header information to amplitude data, onwhich the zero compressing section 302 has performed zero compression,and properly performs blocking thereon. Then, the blocking section 303outputs the amplitude data as compression data. The outputtedcompression data is transmitted to a transmission line or recorded in arecording medium.

FIG. 26 is a diagram showing an example of a format of blockedcompression data. FIG. 26(a) shows a format of the whole compressiondata. As shown in FIG. 26(a) in the compression data, compressioninformation inputted from the zero compressing section 302 is formed soas to follow header information of 64 bytes. The compression data isdata provided in 9 bits.

FIG. 26(b) shows the format of the compression information. A sound part(data which is not replaced by the zero compressing section 302) iscomposed of compression information outputted from the rounding section204. Further, a mute part (data replaced by the zero compressing section302) is composed of a pair of −0 (data raising “1” only on a sign bit)and the number of clocks in successive zero data.

FIG. 27 is a diagram showing an example of a configuration of adecompressing device according to Embodiment 4 for the compressingdevice configured as FIG. 25. Besides, in FIG. 27, members indicated bythe same reference numerals as those of FIG. 19 have the same functionsand the overlapping explanation is omitted.

As shown in FIG. 27, the decompressing device of the present embodimentis constituted by an inverse blocking section 311, an inverse roundingsection 212, an interpolating section 214, and a format convertingsection 312. In this case, the interpolating section 214 corresponds tointerpolating means of the present invention.

The inverse blocking section 311 retrieves compression information fromcompression data based on header information included in the blockedcompression data of FIG. 26. At this point, when data of −1(H80) isdetected, zero data is reproduced by the number of clocks which aresubsequently recorded. In this way, the inverse blocking section 311includes zero decompressing means of the present invention.

The format converting section 312 converts the format of decompressiondata, which is outputted from the interpolating section 214, to theoriginal format before compression. For example, the output data fromthe interpolating section 214 is converted to a signal of WAV (wave)format. Further, at need, a signal after the format conversion issubjected to D/A conversion and is outputted.

The compressing device and the decompressing device configured thusaccording to the present embodiment are constituted by a CPU or acomputer system comprising an MPU, a ROM, and a RAM, and the functionsof the devices can be achieved by operating programs stored in the ROMand the RAM.

Moreover, the compressing device and the decompressing device configuredthus according to the present embodiment can be partly or entirelyconstituted by combining logic circuits like hardware.

As discussed above in detail, according to Embodiment 4, thinned-outdata is obtained in the thinning section 202 on the compression partbased on a digital basic function serving as the original of a samplingfunction of a finite base differentiable once or more times over thewhole range, thereby achieving a compression ratio of 8.

Additionally, since the rounding operation 204 rounds lower-order bitsof thinned-out data (amplitude data) produced by the thinning section202, the data length can be shortened by several bits per word, therebyachieving a substantial reduction in data amount.

As compared with Embodiment 3, although amplitude data is not reduced bylinear compression, the necessity for timing data can be completelyeliminated. Therefore, it is possible to shorten a data length to 9 bitsper unit and thus an amount of data can be reduced accordingly.

Further, the zero compression is performed instead of linear compressionin the zero compressing section 302, so that zero data having a certaintime interval can be compressed to a pair of “−0” and the number ofclocks, thereby further reducing the data amount. In addition, sincedata having a small absolute value is replace with zero data in advancein the mute processing section 201, it is possible to achieve a largerreduction in data amount in the zero compression.

As is apparent from above description, the present embodiment canentirely achieve an extremely high compression ratio (about 8 to severalhundreds).

Additionally, in the interpolating section 214 on the decompressionpart, interpolation data is obtained by using the same function as thedigital basic function used in the thinning section 202 on thecompression part, so that the original data before compression can bereproduced with substantial fidelity.

Further, while the rounding operation is performed on the compressionpart, most amplitude data to be rounded concentrate on a data areaaround the center of the whole data area but few data appear in a dataarea around the ends. Thus, even when lower-order bits are reduced, itis possible to eliminate the influence on the quality of reproduced dataon the decompression part.

Furthermore, in the present embodiment, the rounding operation isperformed so that a data value before the rounding operation and a datavalue after the rounding operation have a non-linear relationship.Hence, when voice is used as data to be compressed, output data valuesare concentrated on a data area around the center where most data appearin the whole data area indicating voice data of audible tone, and theinfluence of the rounding operation can be reduced, thereby furtherreducing the influence on the quality of reproduced voice on thedecompression part.

Besides, the present embodiment makes it possible to compress anddecompress data to be compressed as it is on a time base withoutperforming any time/frequency conversion. In addition, the compressionand decompression can be performed only by extremely simple fouroperations. Further, as compared with Embodiment 3, the operation oflinear compression can be also omitted. Therefore, the operations arenot complicated as a whole and the configuration can be also simplified.Moreover, when compression data is transmitted from the compression partand is reproduced on the decompression part, inputted compression datacan be sequentially processed and reproduced by extremely simple linearinterpolation on a time base, thereby achieving a real-time operation.

As described above, the present embodiment makes it possible to achievea higher compression ratio while maintaining the extremely preferablequality of reproduced data. In addition, the operation time can beshortened and the arithmetic circuit can be simplified.

The above-described compressing and decompressing methods according toEmbodiments 1 to 4 can be obtained by any of a hardware structure, aDSP, and software. For example, when the methods are realized bysoftware, the compressing device and the decompressing device areactually constituted by a CPU or an MPU, a RAM, a ROM, and so on of acomputer and are realized by operating programs stored in the RAM andthe ROM.

Therefore, the devices are realized by recording programs, which areexecuted so that the computer performs the functions of the presentembodiment, in a recording medium such as a CD-ROM and reading theprograms in the computer. As a recording medium for recording theprograms, a floppy disk, a hard disk, a magnetic tape, an optical disk,a magneto-optical disk, a DVD, a nonvolatile memory card, and so on areavailable other than a CD-ROM. Further, the devices are realized also bydownloading the programs to a computer via a network such as Internet.

In addition to the case where the computer executes supplied programs torealize the functions of the above-described embodiments, in the casewhere the functions of the above-described embodiments are achieved byexecuting the programs in coordination with the OS (operating system) orother application software and so on which are operated in the computerand in the case where the functions of the above-described embodimentsare achieved by performing some or all the operations of the suppliedprograms by the feature expansion board and the feature expansion unitof the computer, the programs are included in the embodiments of thepresent invention.

Further, the above-described embodiments just described specificexamples for practicing the present invention and shall not limit theinterpretation of the technical scope of the present invention. Namely,the present invention can be practiced in various forms withoutdeparting from the spirit and the main characteristics of the invention.

As described above, the present invention can achieve both of anincreased compression ratio and improved quality of reproduced data. Inaddition, the compressing and decompressing operations of a signal canbe simplified to shorten the processing time and the configuration forachieving the simplification can be also simplified.

INDUSTRIAL APPLICABILITY

The present invention provides completely new compressing anddecompressing methods of improving a compression ratio and the qualityof reproduced data. The present invention is effective for simplifyingcompressing and decompressing operations of a signal to shorten theprocessing time and for simplifying the configuration for realizing thesimplification.

1. A compressing device, comprising: delay circuits of several stagesfor sequentially delaying each sampling data inputted therein insequence; and a multiplying/adding circuit for performing weightedaddition on data outputted from each of the delay circuits, the weightedaddition being performed according to a value of a digital basicfunction, whereby thinned-out data is produced from the sequentiallyinputted sampling data.
 2. A compressing device, comprising: delaycircuits of four stages for sequentially delaying each sampling datainputted therein in sequence; and a multiplying/adding circuit forperforming weighted addition on data outputted from each of the delaycircuits, the weighted addition being performed according to a value ofa digital basic function, whereby thinned-out data is produced from thesequentially inputted sampling data.
 3. The compressing device accordingto claim 2, wherein the multiplying/adding circuit comprises: a firstmultiplying/adding circuit for adding output data from the delaycircuits of the second and third stages and then multiplying the addeddata by 9; a second multiplying/adding circuit for adding output datafrom the delay circuits of the first and fourth stages and thenmultiplying the added data by −1; and a third multiplying/adding circuitfor adding output data from the first multiplying/adding circuit andoutput data from the second multiplying/adding circuit and thenmultiplying the added data by 1/16.
 4. The compressing device accordingto claim 2, wherein the delay circuits of the four stages and themultiplying/adding circuits are designed as a thinning-out circuit, andin the compressing device, at least two thinning-out circuits areconnected so as to have a cascade connection.
 5. A compressing device,comprising: delay circuits of seven stages for sequentially delayingeach sampling data inputted therein in sequence; and amultiplying/adding circuit for performing weighted addition on dataoutputted from each of the delay circuits, the weighted addition beingperformed according to a value of a digital basic function, wherebythinned-out data is produced from the sequentially inputted samplingdata.
 6. The compressing device according to claim 5, wherein themultiplying/adding circuit comprises: a first multiplying/adding circuitfor adding output data from the delay circuits of the first and seventhstages and then multiplying the added data by −1; a secondmultiplying/adding circuit for adding output data from the delaycircuits of the third and fifth stages and then multiplying the addeddata by 9; a multiplying circuit for multiplying output data from thedelay circuit of the fourth stage by 16; and a third multiplying/addingcircuit for adding output data from the first multiplying/addingcircuit, output data from the second multiplying/adding circuit, andoutput data from the multiplying circuit, and then multiplying the addeddata by 1/32.
 7. The compressing device according to claim 5, whereinthe delay circuits of the seven stages and the multiplying/addingcircuits are designed as a thinning-out circuit, and in the compressingdevice, at least two thinning-out circuits are connected so as to have acascade connection.
 8. A compressing device, wherein sampling data issequentially inputted therein as a target of compression, and thenweighted addition is performed on sampling data on a target sample pointand sampling data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function, whereby thinned-out data is produced from thesequentially inputted sampling data.
 9. A compressing device into whichsampling data can be inputted in sequence as a target of compression,the device comprising: thinning-out means for performing weightedaddition with respect to the inputted sampling data to producethinned-out data therefrom, in which the weighted addition is performedon sampling data on a target sample point and sampling data on severalsample points around said target sample point, the weighted additionbeing performed according to a value of a digital basic function;sampling point detecting means for detecting a sampling point using thethinned-out data produced by the thinning-out means, in which a samplepoint, where an error between each data value on a straight lineconnecting two thinned-out data and a thinned-out data value on the samesample point as that of said data value on the straight line is equal toor smaller than a predetermined value, is detected as the samplingpoint; and compression data producing means for producing, in the formof compression data, a pair of discrete amplitude data on each of thedetected sampling points and timing data indicating a time intervalbetween the detected sampling points.
 10. The compressing deviceaccording to claim 9, further comprising replacing means for replacingsampling data with zero data, in which among the discrete sampling datasuccessively inputted as a target of compression, the sampling data tobe replaced has an absolute value smaller than a predetermined value,wherein through the replacing means the inputted sampling data is fed tothe thinning-out means.
 11. The compressing device according to claim 9,further comprising replacing means for rounding by a predetermined valuean absolute value of the sampling data inputted as a target ofcompression, as well as for performing a data replacement process,wherein in the data replacement process, the replacing means replacessampling data with zero data, in which among the sampling data inputtedas a target of compression, the sampling data to be replaced hasabsolute value smaller than a predetermined value, and wherein throughthe replacing means the inputted sampling data is fed to thethinning-out means.
 12. The compressing device according to claim 9,further comprising rounding means for rounding lower-order bits ofamplitude data on each of the sampling points detected by the samplingpoint detecting means, wherein the compression data producing meansproduces, in the form of the compression data, a pair of the roundedamplitude data on each of the detected sampling points and timing dataindicating a time interval between the detected sampling points.
 13. Thecompressing device according to claim 12, wherein the rounding operationby the rounding means is performed according to an operation in whichdata values before and after the rounding operation have a non-linearrelationship.
 14. The compressing device according to claim 13, whereinthe operation having the non-linear relationship is an operation basedon a logarithmic function or a function approximated thereto.
 15. Acompressing device, into which sampling data can be successivelyinputted as a target of compression, the device comprising: replacingmeans for replacing sampling data with zero data, in which among thediscrete sampling data successively inputted as a target of compression,the sampling data to be replaced has an absolute value smaller than apredetermined value; and thinning-out means for performing weightedaddition with respect to the sampling data sequentially inputted thereinfrom the replacing means, in which the weighted addition is performedsampling data on a target sample point and sampling data on severalsample points around said target sample point, the weighted additionbeing performed according to a value of a digital basic function,whereby thinned-out data is produced from the sampling data.
 16. Thecompressing device according to claim 15, further comprising roundingmeans for rounding a lower-order bit of the thinned-out data produced bythe thinning-out means.
 17. The compressing device according to claim16, wherein the rounding operation by the rounding means is performedaccording to an operation in which data values before and after therounding operation have a non-linear relationship.
 18. The compressingdevice according to claim 17, further comprising zero compressing meansfor performing a zero compressing process with respect to thethinned-out data outputted from the rounding means, wherein the zerocompressing process is performed when a predetermined number or more ofdata having absolute values of zero are successively outputted from therounding means, and wherein in the zero compressing process, a set ofsaid predetermined number of zero data is replaced with a pair of avalue of −0 and a value indicating the number of successive zero data,and then the thinned-out data including a replacement result isoutputted from the zero compressing means.
 19. A compressing device,into which sampling data can be inputted in sequence as a target ofcompression, the device comprising: thinning-out means for performingweighted addition with respect to the inputted sampling data to producethinned-out data therefrom, in which the weighted addition is performedon sampling data on a target sample point and sampling data on severalsample points around said target sample point, the weighted additionbeing performed according to a value of a digital basic function; androunding means for rounding a lower-order bit of the producedthinned-out data.
 20. The compressing device according to claim 19,wherein the rounding operation by the rounding means is performedaccording to an operation in which data values before and after therounding operation have a non-linear relationship.
 21. The compressingdevice according to claim 20, further comprising zero compressing meansfor performing a zero compressing process with respect to thethinned-out data outputted from the rounding means, wherein the zerocompressing process is performed when a predetermined number or more ofdata having absolute values of zero are successively outputted from therounding means; and wherein in the zero compressing process, a set ofsaid predetermined number of zero data is replaced with a pair of avalue of −0 and a value indicating the number of successive zero data,and then the thinned-out data including a replacement result isoutputted from the zero compressing means.
 22. A compressing device,into which sampling data can be successively inputted as a target ofcompression, the device comprising: replacing means for replacingsampling data with zero data, in which among the discrete sampling datasuccessively inputted as a target of compression, the sampling data tobe replaced has an absolute value smaller than a predetermined value;rounding means for performing a rounding operation on the sampling dataoutputted from the replacing means to round lower-order bits thereof,the rounding operation being performed according to an operation inwhich data values before and after the rounding operation have anon-linear relationship; and zero compressing means for performing azero compressing process with respect to the sampling data outputtedfrom the rounding means, wherein the zero compressing process isperformed when a predetermined number or more of data having absolutevalues of zero are successively outputted from the rounding means, andwherein in the zero compressing process a set of said predeterminednumber of zero data is replaced with a pair of a value of -0 and a valueindicating the number of successive zero data, and then data including areplacement result is outputted from the zero compressing means.
 23. Acompressing device, into which sampling data can be successivelyinputted as a target of compression, the device comprising: roundingmeans for performing a rounding operation on the successively inputtedsampling data to round lower-order bits thereof, the rounding operationbeing performed according to an operation in which data values beforeand after the rounding operation have a non-linear relationship; andzero compressing means for performing a zero compressing process withrespect to the sampling data outputted from the rounding means, whereinthe zero compressing process is performed when a predetermined number ormore of data having absolute values of zero are successively outputtedfrom the rounding means, and wherein in the zero compressing process aset of said predetermined number of zero data is replaced with a pair ofa value of -0 and a value indicating the number of successive zero data,and then data including a replacement result is outputted from the zerocompressing means.
 24. A compressing method, comprising the steps of:sequentially inputting sampling data as a target of compression; andperforming weighted addition with respect to the inputted sampling data,the weighted addition being performed on sampling data on a targetsample point and sampling data on several sample points around saidtarget sample point, and the weighted addition being performed accordingto a value of a digital basic function, whereby thinned-out data isproduced from the sequentially inputted sampling data.
 25. Thecompressing method according to claim 24, wherein the digital basicfunction is a function having a data value changing to −1, 1, 8, 8, 1,and −1 on each clock.
 26. The compressing method according to claim 24,wherein the digital basic function is a function having a data valuechanging to −1, 0, 9, 16, 9, 0, and −1 on each clock, the function beingproduced by shifting the digital basic function in claim 25 by one clockand then adding the digital basic functions before and after the shift.27. The compressing method according to claim 24, wherein when samplingdata on four successive sample points are denoted by A, B, C and D,respectively, in the weighted addition two sampling data B and C ontarget sample points are replaced with one thinned-out data according toan operation of (9(B+C)−(A+D))/16, and the same operation issequentially performed while the target sample points where two samplingdata are to be replaced are shifted by two sample points.
 28. Thecompressing method according to claim 24, wherein when sampling data onseven successive sample points are denoted by A, B, C, D, E, F, and G,respectively, in the weighted addition the sampling data D on a targetsample point is replaced with one thinned-out data according to anoperation of (16D+9(C+E)−(A+G))/32, and the same operation issequentially performed while the target sample point is shifted by twosample points.
 29. The compressing method according to claim 24, furthercomprising the step of further performing weighted addition with respectto the thinned-out data already produced through the first weightedaddition, in which the second weighted addition is performed onthinned-out data on a target sample point and thinned-out data onseveral sample points around said target sample point, the secondweighted addition being performed according to a value of the digitalbasic function.
 30. A compressing method, comprising the steps of:sequentially inputting sampling data as a target of compression;performing weighted addition with respect to the inputted sampling data,the weighted addition being performed on sampling data on a targetsample point and sampling data on several sample points around saidtarget sample point, and the weighted addition being performed accordingto a value of a digital basic function, whereby thinned-out data isproduced from the sequentially inputted sampling data; determining asampling point using the produced thinned-out data, in which a samplepoint, where a difference value between each data value on a straightline connecting two thinned-out data and a thinned-out data value on thesame sample point as that of said data value on the straight line isequal to or smaller than a predetermined value, is detected as thesampling point; and producing, in the form of compression data, a pairof discrete amplitude data on each of the detected sampling points andtiming data indicating a time interval between the detected samplingpoints.
 31. The compressing method according to claim 30, furthercomprising the step of replacing sampling data with zero data, in whichamong the discrete sampling data successively inputted as a target ofcompression, the sampling data to be replaced has an absolute valuesmaller than a predetermined value, wherein the weighted addition beingperformed on data subjected to the data replacement.
 32. The compressingmethod according to claim 30, further comprising the step of roundinglower-order bits of amplitude data on each of the detected samplingpoints, wherein in the compression data producing step, a pair of therounded amplitude data on each of the detected sampling points andtiming data indicating a time interval between the detected samplingpoints is produced in the form of said compression data.
 33. Acompressing method, comprising the steps of: sequentially inputtingsampling data as a target of compression; replacing sampling data withzero data, in which among the discrete sampling data successivelyinputted as a target of compression, the sampling data to be replacedhas an absolute value smaller than a predetermined value; and performingweighted addition with respect to the successive sampling data subjectedto the data replacement process, the weighted addition being performedon sampling data on a target sample point and sampling data on severalsample points around said target sample point, and the weighted additionbeing performed according to a value of a digital basic function,whereby thinned-out data is produced from the sequentially inputtedsampling data.
 34. The compressing method according to claim 33, furthercomprising the step of rounding a lower-order bit of the thinned-outdata produced by the weighted addition step.
 35. The compressing methodaccording to claim 34, wherein the rounding operation step is performedaccording to an operation in which data values before and after therounding operation have a non-linear relationship.
 36. The compressingmethod according to claim 35, further comprising the step of performinga zero compressing process with respect to the thinned-out datasubjected to the rounding operation, wherein the zero compressingprocess is performed when a predetermined number or more of data havingabsolute values of zero are successively outputted in the roundingoperation; and wherein in the zero compressing process a set of saidpredetermined number of zero data is replaced with a pair of a value of−0 and a value indicating the number of successive zero data, and thenthe thinned-out data including a replacement result is outputted.
 37. Acompressing method, comprising the steps of: sequentially inputtingsampling data as a target of compression; performing weighted additionwith respect to the sampling data successively inputted as a target ofcompression, the weighted addition being performed on sampling data on atarget sample point and sampling data on several sample points aroundsaid target sample point, and the weighted addition being performedaccording to a value of a digital basic function, whereby thinned-outdata is produced from the sequentially inputted sampling data; androunding a lower-order bit of the thinned-out data produced by theweighted addition.
 38. The compressing method according to claim 37,wherein the rounding operation step is performed according to anoperation in which data values before and after the rounding operationhave a non-linear relationship.
 39. The compressing method according toclaim 38, further comprising the step of performing a zero compressingprocess with respect to the thinned-out data subjected to the roundingoperation, wherein the zero compressing process is performed when apredetermined number or more of data having absolute values of zero aresuccessively outputted in the rounding operation, and wherein in thezero compressing process a set of said predetermined number of zero datais replaced with a pair of a value of −0 and a value indicating thenumber of successive zero data, and then the thinned-out data includinga replacement result is outputted.
 40. A compressing means method,comprising the steps of: sequentially inputting sampling data as atarget of compression; replacing sampling data with zero data, in whichamong the discrete sampling data successively inputted as a target ofcompression, the sampling data to be replaced has an absolute valuesmaller than a predetermined value; rounding a lower-order bit of thesampling data subjected to the data replacement process, the roundingoperation step being performed according to an operation in which datavalues before and after the rounding operation have a non-linearrelationship; and performing a zero compressing process with respect tothe sampling data subjected to the rounding operation, wherein the zerocompressing process is performed when a predetermined number or more ofdata having absolute values of zero are successively outputted in therounding operation, and wherein in the zero compressing process a set ofsaid predetermined number of zero data is replaced with a pair of avalue of −0 and a value indicating the number of successive zero data,and then data including a replacement result is outputted.
 41. Acompressing method, comprising the steps of: sequentially inputtingsampling data as a target of compression; rounding a lower-order bit ofthe discrete sampling data successively inputted, the rounding operationbeing performed according to an operation in which data values beforeand after the rounding operation have a non-linear relationship; andperforming a zero compressing process with respect to the sampling datasubjected to the rounding operation, wherein the zero compressingprocess is performed when a predetermined number or more of data havingabsolute values of zero are successively outputted in the roundingoperation, and wherein in the zero compressing process aset of saidpredetermined number of zero data is replaced with a pair of a value of−0 and a value indicating the number of successive zero data, and thendata including a replacement result is outputted.
 42. A compressingprogram, which makes a computer to function as each means in claim 9.43. A compressing program, which makes a computer to function as eachmeans in claim
 15. 44. A compressing program, which makes a computer tofunction as each means in claim
 19. 45. A compressing program, whichmakes a computer to function as each means in claim
 22. 46. Acompressing program, which makes a computer to function as each means inclaim
 23. 47. A compressing program, which makes a computer to performthe steps of the compressing method claimed in claim
 24. 48. A recordmedium readable by a computer, on which a program for making thecomputer to function as each means in claim 9 is recorded.
 49. A recordmedium readable by a computer, on which a program for making thecomputer to execute each of the steps of the compressing method claimedin claim 24 is recorded.
 50. A decompressing device, comprising: delaycircuits of several stages into which discrete thinned-out data producedby a compressing device claimed in claim 1 can be inputted, each of thedelay circuits delaying the inputted thinned-out data in sequence; and amultiplying/adding circuit for performing weighted addition on dataoutputted from each of the delay circuits, the weighted addition beingperformed according to a value of a digital basic function, wherebyinterpolation data for the thinned-out data is produced.
 51. Thedecompressing device according to claim 50, wherein the delay circuitsand the multiplying/adding circuit are designed as an oversamplingcircuit, and in the decompressing device, at least two oversamplingcircuits are connected so as to have a cascade connection.
 52. Adecompressing device, comprising: delay circuits of three stages intowhich discrete thinned-out data produced by a compressing device claimedin claim 2 can be inputted, each of the delay circuits delaying theinputted thinned-out data in sequence; and a multiplying/adding circuitfor performing weighted addition on data outputted from each of thedelay circuits, the weighted addition being performed according to avalue of a digital basic function, whereby interpolation data for thethinned-out data is produced
 53. The decompressing device according toclaim 52, wherein the multiplying/adding circuit comprises: a firstmultiplier for multiplying output data from the delay circuit of thefirst stage by −1; a second multiplier for multiplying output data fromthe delay circuit of the second stage by 8; a third multiplier formultiplying output data from the delay circuit of the third stage by −1;a first switching circuit for selectively outputting any one of datafrom the delay circuit of the first stage and data from the firstmultiplier; a second switching circuit for selectively outputting anyone of data from the delay circuit of the third stage and data from thethird multiplier; and an adder for adding output data from the secondmultiplier, output data from the first switching circuit, and outputdata from the second switching circuit.
 54. The decompressing deviceaccording to claim 52, wherein the multiplying/adding circuit comprises:a first multiplying/adding circuit which includes a first multiplier formultiplying output data from the delay circuit of the first stage by −1;a second multiplier for multiplying output data from the delay circuitof the second stage by 8; and an adder for adding output data from thefirst multiplier, output data from the second multiplier, and outputdata from the delay circuit of the third stage; a secondmultiplying/adding circuit which includes a third multiplier formultiplying output data from the delay circuit of the second stage by 8;a fourth multiplier for multiplying output data from the delay circuitof the third stage by −1; and an adder for adding output data from thethird multiplier, output data from the fourth multiplier, and outputdata from the delay circuit of the first stage; and a switching circuitfor selectively outputting any one of data from the firstmultiplying/adding circuit and data from the second multiplying/addingcircuit.
 55. The decompressing device according to claim 52, wherein themultiplying/adding circuit comprises: a first multiplier for multiplyingoutput data from the delay circuit of the first stage by −1; a secondmultiplier for multiplying output data from the delay circuit of thesecond stage by 8; a third multiplier for multiplying output data fromthe delay circuit of the third stage by −1; a first adder for addingoutput data from the first multiplier, output data from the secondmultiplier, and output data from the delay circuit of the third stage; asecond adder for adding output data from the second multiplier, outputdata from the third multiplier, and output data from the delay circuitof the first stage; and a switching circuit for selectively outputtingany one of data from the first adder and data from the second adder. 56.The decompressing device according to claim 52, wherein the delaycircuits of the three stages and the multiplying/adding circuit aredesigned as an oversampling circuit, and in the decompressing device atleast two oversampling circuits are connected so as to have a cascadeconnection.
 57. A decompressing device, comprising: delay circuits ofseveral stages into which discrete thinned-out data produced by acompressing device claimed in claim 1 can be inputted, each of the delaycircuits delaying the inputted thinned-out data in sequence; thinned-outdata outputted from each of the delay circuits to produce interpolationdata for the thinned-out data, the weighted addition being performedaccording to a value of a digital basic function; and an averagingcircuit for producing average data of adjacent interpolation data valuesoutputted from the multiplying/adding circuit.
 58. The decompressingdevice according to claim 57, wherein the delay circuits of the severalstages and the multiplying/adding circuit are designed as anoversampling circuit, and in the decompressing device at least twooversampling circuits are connected so as to have a cascade connection.59. A decompressing device, comprising: delay circuits of four stagesinto which discrete thinned-out data produced by a compressing deviceclaimed in claim 2 can be inputted, each of the delay circuits delayingthe inputted thinned-out data in sequence; and a multiplying/addingcircuit for performing weighted addition on data outputted from each ofthe delay circuits to produce interpolation data for the thinned-outdata, the weighted addition being performed according to a value of adigital basic function.
 60. The decompressing device according to claim59, wherein the multiplying/adding circuit comprises: a first multiplierfor multiplying output data from the delay circuit of the first stage by−1; a second multiplier for multiplying output data from the delaycircuit of the second stage by 9; a third multiplier for multiplyingoutput data from the delay circuit of the third stage by 9; a fourthmultiplier for multiplying output data from the delay circuit of thefourth stage by −1; an adder for adding output data from the first tofourth multipliers; and a switching circuit for selectively outputtingany one of data from the adder and the thinned-out data to be inputtedinto the delay circuit of the first stage.
 61. The decompressing deviceaccording to claim 59, wherein the multiplying/adding circuit comprises:a first adder for adding output data from the delay circuit of the firststage and output data from the delay circuit of the fourth stage; asecond adder for adding output data from the delay circuit of the secondstage and output data from the delay circuit of the third stage; a firstmultiplier for multiplying output data from the first adder by −1; asecond multiplier for multiplying output data from the second adder by9; a third adder for adding output data from the first adder and outputdata from the second adder; and a switching circuit for selectivelyoutputting any one of data from the third adder and the thinned-out datato be inputted into the delay circuit of the first stage.
 62. Thedecompressing device according to claim 59, wherein the delay circuitsof the four stages and the multiplying/adding circuit are designed as anoversampling circuit, and in the decompressing device at least twooversampling circuits are connected so as to have a cascade connection.63. A decompressing device, comprising: delay circuits of five stagesinto which discrete thinned-out data produced by a compressing deviceclaimed in claim 5 can be inputted, each of the delay circuits delayingthe inputted thinned-out data in sequence; and a multiplying/addingcircuit for performing weighted addition on the thinned out dataoutputted from each of the delay circuits to produce interpolation datafor the thinned-out data, the weighted addition being performedaccording to a value of a digital basic function.
 64. The decompressingdevice according to claim 63, wherein the multiplying/adding circuitcomprises: a first multiplying/adding circuit which includes a firstmultiplier for multiplying output data from the delay circuit of thefirst stage by −1; a second multiplier for multiplying output data fromthe delay circuit of the second stage by 9; a third multiplier formultiplying output data from the delay circuit of the third stage by 25;a fourth multiplier for multiplying output data from the delay circuitof the fourth stage by −1; and an adder for adding output data from thefirst to fourth multipliers; a second multiplying/adding circuit whichincludes a fifth multiplier for multiplying output data from the delaycircuit of the second stage by −1; a sixth multiplier for multiplyingoutput data from the delay circuit of the fourth stage by 9; a seventhmultiplier for multiplying output data from the delay circuit of thefifth stage by −1; and an adder for adding output data from the thirdmultiplier and the fifth to seventh multipliers; and a switching circuitfor selectively outputting any one of data from the firstmultiplying/adding circuit and data from the second multiplying/addingcircuit.
 65. A decompressing device, wherein thinned-out data isinputted therein sequentially, and then interpolation data for thethinned-out data inputted sequentially is produced by performingweighted addition on thinned-out data on a target sample point andthinned-out data on several sample points around said target samplepoint, in which the weighted addition is performed according to a valueof a digital basic function.
 66. A decompressing device, comprising:first interpolating means for performing an interpolation process withrespect to thinned-out data produced by a compressing device claimed inclaim 9, in which in the interpolation process, timing data andamplitude data on each sampling point are used to produce firstinterpolation data for interpolating between one amplitude data and theother amplitude data which have a time interval indicated by the timingdata; and second interpolating means for producing second interpolationdata for the produced first interpolation data by performing a furtherinterpolation process with respect to the produced first interpolationdata, in which in the further interpolation process, weighted additionis performed on interpolation data on a target sample point andinterpolation data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.
 67. A decompressing device, comprising: inverserounding means for performing an inverse rounding operation on amplitudedata on each sampling point in compression data produced by acompressing device claimed in claim 12, the inverse rounding operationbeing performed in a manner reversed from a rounding operation performedduring compression by the compression device; first interpolating meansfor performing an interpolation process using both of timing data in thecompression data and the amplitude data outputted from the inverserounding means, in which through the interpolation process the firstinterpolation means produces first interpolation data for interpolatingbetween one amplitude data and the other amplitude data which have atime interval indicated by the timing data; and second interpolatingmeans for producing second interpolation data for the produced firstinterpolation data by performing weighted addition with respect to theproduced first interpolation data, in which the weighted addition isperformed on first interpolation data on a target sample point and firstinterpolation data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.
 68. The decompressing device according to claim67, wherein the operation reversed from the rounding operation isperformed according to an operation in which data values before andafter the inverse rounding operation have a non-linear relationship. 69.The decompressing device according to claim 68, wherein the operationhaving the non-linear relationship is an operation based on anexponential function or a function approximated thereto.
 70. Adecompressing device, comprising interpolating means for performing aninterpolation process with respect to discrete thinned-out data producedby a compressing device claimed in claim 15 to produce interpolationdata for the discrete thinned-out data, wherein in the interpolationprocess, weighted addition is performed on thinned-out data on a targetsample point and thinned-out data on several sample points around saidtarget sample point, the weighted addition being performed according toa value of a digital basic function.
 71. A decompressing device,comprising: inverse rounding means for performing an inverse roundingoperation on discrete thinned-out data produced through a roundingoperation by a compressing device claimed in claim 16, the inverserounding operation being performed in a manner reversed from a roundingoperation performed during the compression by the compression device;and interpolating means for performing an interpolation process withrespect to the discrete thinned-out data outputted from the inverserounding means to produce interpolation data for the discretethinned-out data, wherein in the interpolation process, weightedaddition is performed on thinned-out data on a target sample point andthinned-out data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.
 72. A decompressing device, comprising: inverserounding means for performing an inverse rounding operation on discretethinned-out data produced through a rounding operation by a compressingdevice claimed in claim 19, the inverse rounding operation beingperformed in a manner reversed from a rounding operation performedduring compression by the compression device; and interpolating meansfor performing an interpolation process with respect to the discretethinned-out data outputted from the inverse rounding means to produceinterpolation data for the discrete thinned-out data, wherein in theinterpolation process, weighted addition is performed on thinned-outdata on a target sample point and thinned-out data on several samplepoints around said target sample point, the weighted addition beingperformed according to a value of a digital basic function.
 73. Adecompressing device, comprising: zero decompressing means forperforming a zero decompressing process with respect to thinned-out dataproduced by a compressing device claimed in claim 18, in which when a −0value is detected in the thinned-out data, a corresponding number ofsuccessive zero data are reproduced through the zero decompressingprocess; inverse rounding means for performing an inverse roundingoperation on the discrete thinned-out data including the zero datareproduced by the zero decompressing means, the inverse roundingoperation being performed in a manner reversed from a rounding operationperformed during compression by the compressing device; andinterpolating means for performing an interpolation process with respectto the discrete thinned-out data outputted from the inverse roundingmeans to produce interpolation data for said discrete thinned-out data,in which in the interpolation process, weighted addition is performed onthinned-out data on a target sample point and thinned-out data onseveral sample points around said target sample point, the weightedaddition being performed according to a value of a digital basicfunction.
 74. A decompressing device, comprising: zero decompressingmeans for performing a zero decompressing process with respect tothinned-out data produced by a compressing device claimed in claim 21,in which when a −0 value is detected in the thinned-out data, acorresponding number of successive zero data are reproduced through thezero decompressing process; inverse rounding means for performing aninverse rounding operation on the discrete thinned-out data includingthe zero data reproduced by the zero decompressing means, the inverserounding operation being performed in a manner reversed from a roundingoperation performed during compression by the compressing device; andinterpolating means for performing an interpolation process with respectto the discrete thinned-out data outputted from the inverse roundingmeans to produce interpolation data for said discrete thinned-out data,in which in the interpolation process, weighted addition is performed onthinned-out data on a target sample point and thinned-out data onseveral sample points around said target sample point, the weightedaddition being performed according to a value of a digital basicfinction.
 75. A decompressing device, comprising: zero decompressingmeans for performing a zero decompressing process with respect tothinned-out data produced by a compressing device claimed in claim 22,in which when a −0 value is detected in the thinned-out data, acorresponding number of successive zero data are reproduced through thezero decompressing process; and inverse rounding means for performing aninverse rounding operation on the discrete thinned-out data includingthe zero data reproduced by the zero decompressing means, the inverserounding operation being performed in a manner reversed from a roundingoperation performed during compression by the compressing device.
 76. Adecompressing device, comprising: zero decompressing means forperforming a zero decompressing process with respect to thinned-out dataproduced by a compressing device claimed in claim 23, in which when a −0value is detected in the thinned-out data, a corresponding number ofsuccessive zero data are reproduced through the zero decompressingprocess; and inverse rounding means for performing an inverse roundingoperation on the discrete thinned-out data including the zero datareproduced by the zero decompressing means, the inverse roundingoperation being performed in a manner reversed from a rounding operationperformed during compression by the compressing device.
 77. Adecompressing method, comprising the steps of: successively inputtingthinned-out data produced by a compressing method claimed in claim 24;and performing an interpolation process with respect to the inputteddiscrete thinned-out data to produce interpolation data for saiddiscrete thinned-out data, in which in the interpolation process,weighted addition is performed on thinned-out data on a target samplepoint and thinned-out data on several sample points around said targetsample point, the weighted addition being performed according to a valueof a digital basic function.
 78. The decompressing method according toclaim 77, wherein each discrete thinned-out data is replaced with twointerpolation data each of which has been produced by the weightedaddition according to a value of the digital basic function.
 79. Thedecompressing method according to claim 78, further comprising the stepof performing an averaging operation with respect to the interpolationdata produced through the weighted addition, wherein the averagingoperation is performed on adjacent discrete interpolation data.
 80. Thedecompressing method according to claim 77, wherein another weightedaddition is further performed with respect to the interpolation dataalready produced through the weighted addition, in which said furtherweighted addition is performed on interpolation data on a target samplepoint and interpolation data on several sample points around said targetsample point, the further weighted addition being performed according toa value of the digital basic function, whereby further interpolationdata for the already produced interpolation data on said target samplepoint is produced.
 81. A decompressing method, comprising the steps of:performing a first interpolation process with respect to compressiondata produced by a compressing method claimed in claim 30, in which inthe first interpolation process, timing data and amplitude data on eachsampling point are used to produce first interpolation data forinterpolating between one amplitude data and the other amplitude datawhich have a time interval indicated by the timing data; and performinga second interpolation process with respect to the produced firstinterpolation data to produce second interpolation data for the producedfirst interpolation data, in which another weighted addition isperformed on first interpolation data on a target sample point and firstinterpolation data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.
 81. (canceled)
 82. A decompressing method,comprising the steps of: performing an inverse rounding operation onamplitude data on each sampling point in compression data produced by acompressing method claimed in claim 32, the inverse rounding operationbeing performed in a manner reversed from a rounding operation performedduring compression by the compressing method; performing a firstinterpolation process using both of the amplitude data successivelysubjected to the inverse rounding operation and timing data in thecompression data, in which through the first interpolation process,first interpolation data for interpolating between one amplitude dataand the other amplitude data which have a time interval indicated by thetiming data is produced; and performing a second interpolations processwith respect to the produced first interpolation data, in which in thesecond interpolation process, weighted addition is performed on firstinterpolation data on a target sample point and first interpolation dataon several sample points around said target sample point, the weightedaddition being performed according to a value of a digital basicfunction, whereby second interpolation data for the produced firstinterpolation is produced through the second interpolation process. 83.The decompressing method according to claim 82, the operation reversedfrom the rounding operation is performed according to an operation inwhich data values before and after the inverse rounding operation have anon-linear relationship.
 84. A decompressing method, in which weightedaddition is performed with respect to discrete thinned-out data producedby a compressing method claimed in claim 33, wherein the weightedaddition is performed on thinned-out data on a target sample point andthinned-out data on several sample points around said target samplepoint to produce interpolation data for the discrete thinned-out data,the weighted addition being performed according to a value of a digitalbasic function.
 85. A decompressing method, comprising the steps of:performing an inverse rounding operation on discrete thinned-out dataproduced through a rounding operation by a compressing method claimed inclaim 34, the inverse rounding operation being performed in a mannerreversed from a rounding operation performed during compression by thecompression device; and performing an interpolation process with respectto the discrete thinned-out data subjected to the inverse roundingoperation to produce interpolation data for the discrete thinned-outdata, wherein in the interpolation process, weighted addition isperformed on thinned-out data on a target sample point and thinned-outdata on several sample points around said target sample point, theweighted addition being performed according to a value of a digitalbasic function.
 86. A decompressing method, comprising the steps of:performing an inverse rounding operation on discrete thinned-out dataproduced through a rounding operation by a compressing method claimed inclaim 3 7, the inverse rounding operation being performed in a mannerreversed from a rounding operation performed during the compression bythe compression device; and performing an interpolation process withrespect to the discrete thinned-out data subjected to the inverserounding operation to produce interpolation data for the discretethinned-out data, wherein in the interpolation process, weightedaddition is performed on thinned-out data on a target sample point andthinned-out data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.
 87. A decompressing method, comprising the stepsof: performing a zero decompressing process with respect to thinned-outdata produced by a compressing method claimed in claim 36, in which whena −0 value is detected in the thinned-out data, a corresponding numberof successive zero data are reproduced through the zero decompressingprocess; performing an inverse rounding operation on the discretethinned-out data including the zero data reproduced through the zerodecompressing step, the inverse rounding operation being performed in amanner reversed from a rounding operation performed during thecompression; and performing an interpolation process with respect to thediscrete thinned-out data subjected to the inverse rounding operation toproduce interpolation data for said discrete thinned-out data, in whichin the interpolation process, weighted addition is performed onthinned-out data on a target sample point and thinned-out data onseveral sample points around said target sample point, the weightedaddition being performed according to a value of a digital basicfunction.
 88. A decompressing method, comprising the steps of:performing a zero decompressing process with respect to thinned-out dataproduced by a compressing method claimed in claim 39, in which when a −0value is detected in the thinned-out data, a corresponding number ofsuccessive zero data are reproduced through the zero decompressingprocess; performing an inverse rounding operation on the discretethinned-out data including the zero data reproduced in the zerodecompressing step, the inverse rounding operation being performed in amanner reversed from a rounding operation performed during thecompression; and performing an interpolation process with respect to thediscrete thinned-out data subjected to the inverse rounding step toproduce interpolation data for said discrete thinned-out data, in whichin the interpolation process, weighted addition is performed onthinned-out data on a target sample point and thinned-out data onseveral sample points around said target sample point, the weightedaddition being performed according to a value of a digital basicfunction.
 89. A decompressing method, comprising the steps of:performing a zero decompressing process with respect to thinned-out dataproduced by a compressing method claimed in claim 40, in which when a −0value is detected in the thinned-out data, a corresponding number ofsuccessive zero data are reproduced through the zero decompressingprocess; and performing an inverse rounding operation on the discretethinned-out data including the zero data reproduced in the zerodecompressing step, the inverse rounding operation being performed in amanner reversed from a rounding operation performed during thecompression.
 90. A decompressing method, comprising the steps of:performing a zero decompressing process with respect to thinned-out dataproduced by a compressing method claimed in claim 41, in which when a −0value is detected in the thinned-out data, a corresponding number ofsuccessive zero data are reproduced through the zero decompressingprocess; and performing an inverse rounding operation on the discretethinned-out data including the zero data reproduced in the zerodecompressing step, the inverse rounding operation being performed in amanner reversed from a rounding operation performed during thecompression.
 91. A decompressing program, which makes a computer tofunction as each means in claim
 66. 92. A decompressing program, whichmakes a computer to function as each means in claim
 67. 93. Adecompressing program, which makes a computer to function as each meansin claim
 70. 94. A decompressing program, which makes a computer tofunction as each means in claim
 71. 95. A decompressing program, whichmakes a computer to function as each means in claim
 72. 96. Adecompressing program, which makes a computer to function as each meansin claim
 73. 97. A decompressing program, which makes a computer tofunction as each means in claim
 74. 98. A decompressing program, whichmakes a computer to function as each means in claim
 75. 99. Adecompressing program, which makes a computer to function as each meansin claim
 76. 100. A decompressing program, which makes a computer toexecute each of the steps of a decompressing method claimed in claim 77.101. A record medium readable by a computer, on which a program formaking the computer to function as each means in claim 66 is recorded.102. A record medium readable by a computer, on which a program formaking the computer to execute each of the steps of a decompressingmethod claimed in claim 77 is recorded.
 103. A compressing/decompressingsystem, comprising: a compression part into which sampling data can besequentially inputted as a target of compression to perform acompression process on the sampling data, the compression processcomprising the steps of: sequentially inputting the sampling datatherein; and performing weighted addition with respect to the inputtedsampling data, the weighted addition being performed on sampling data ona target sample point and sampling data on several sample points aroundsaid target sample point, and the weighted addition being performedaccording to a value of a digital basic function, whereby thinned-outdata is produced from the sequentially inputted sampling data; and adecompression part into which said thinned-out data can be inputted insequence to perform a decompression process on the thinned-out data, thedecompression process comprising the steps of: sequentially inputtingthe thinned-out data therein; and performing weighted addition withrespect to the sequentially inputted thinned-out data, the weightedaddition being performed on thinned-out data on a target sample pointand thinned-out data on several sample points around said target samplepoint, and the weighted addition being performed according to a value ofthe digital basic function, whereby interpolation data for thesequentially inputted thinned-out data is produced.
 104. Thecompressing/decompressing system according to claim 103, wherein thecompression process further comprises the step of replacing samplingdata with zero data, in which among the discrete sampling datasuccessively inputted as a target of compression, the sampling data tobe replaced has an absolute value smaller than a predetermined value;and wherein the weighted addition is performed on the sampling datasubjected to the data replacement process.
 105. Thecompressing/decompressing system according to claim 103, wherein thecompression process further comprises the step of performing a roundingoperation to round a lower-order bit of the produced thinned-out data;wherein the decompression process further comprises the step ofperforming an inverse rounding operation on the sequentially inputtedthinned-out data in a manner reversed from the rounding operation; andwherein the weighted addition is performed on the thinned-out datasubjected to the inverse rounding operation.
 106. Thecompressing/decompressing system according to claim 105, wherein therounding operation by the compression part is an operation in which datavalues before and after the rounding operation have a non-linearrelationship; and wherein the compression process further comprises thestep of performing a data replacement process with respect to thethinned-out data produced through the rounding operation, in which inthe replacement process, when a predetermined number or more of datahaving absolute values of zero are outputted in the rounding operation,a set of said predetermined number of zero data is replaced with a pairof a value of −0 and a value indicating the number of successive zero,and then the thinned-out data including a replacement result isoutputted from the compression part.
 107. A decompressing method,comprising the steps of: performing a first interpolation process withrespect to compression data produced by a compressing method claimed inclaim 30, in which in the first interpolation process, timing data andamplitude data on each sampling point are used to produce firstinterpolation data for interpolating between one amplitude data and theother amplitude data which have a time interval indicated by the timingdata; and performing weighted addition with respect to the producedfirst interpolation data to produce second interpolation data for theproduced first interpolation data, in which weighted addition isperformed on interpolation data on a target sample point andinterpolation data on several sample points around said target samplepoint, the weighted addition being performed according to a value of adigital basic function.